High Yield Flashcards
95% confidence intervals
Range of values that is 95% likely to contain the true value
Standard deviation
Value that shows how much variation there is from the mean
P Value
Likelihood that the observed result is due to change
P > 0.05 is not statistically significant
Odds ratio
Ratio of probability that something will happen, to the probability that it won’t happen
Blinding
Patients/clinicians/researchers are prevented from knowing certain information that may lead to conscious or subconscious bias on their part
Concealment of allocation
The procedure for protecting the randomisation process
Person randomising the patient does not know what the treatment allocation will be
Prevents selection bias affecting which patients are give which treatment (the bias the randomisation is designed to avoid)
Intention to treat analysis
Analysis based on the initial treatment intended from allocation,
Intention to treat (ITT) analysis means all patients who were enrolled and randomly allocated to treatment are included in the analysis and are analysed in the groups to which they were randomized, not the treatment eventually administered.
I.e. “once randomized, always analyzed”
Treatment fidelity
How accurately the intervention is reproduced from a manual, protocol or model
Number needed to treat
Number of patients that are needed to be treated with the experimental therapy to prevent one negative outcome
E.g. the number of patients that need to be treated for one of them to benefit compared with a control in a clinical trial
It is defined as the inverse of the absolute risk reduction.
1/Absolute risk reduction
Purpose of randomisation?
To try and ensure that any characteristics of the sample population that may affect the results (confounders) are distributed equally between the 2 study groups, and avoid selection bia
Which type of studies are often affected by recall bias?
Case control
What is recall bias?
The participant either cannot remember back to when they were exposed or their outcome changes their perception of the exposure
Internal validity
Accuracy
How well the study was conducted.
Taking confounders into account and removing bias.
External validity
Generalisability
How well it can be applied to different scenarios, patients, environments.
Case-control studies are prone to recall bias in general
Cohort studies are prone to selection bias in general
List 4 methods that can be used to limit confounding variables.
Restriction:
- Limit participants of study that have possible confounders
- Means less data available
- This method can be difficult with multiple confounders
Matching:
- Make comparison groups (with and without the confounder)
- Used for things like age and sex in case-control studies
Stratification:
- Analyse exposure with sub-groups of the confounder
- Adjust for confounding (if there are few variables)
- Recombine data
- Means sometimes these subgroups have very few participants in them
Multiple variable regression:
- Coefficients are established for the confounder groups
- Allows for better adjustment
Specificity
True negatives (TN)
The probability of a negative, if the patient really is not ill
TN / ( TN + FP)
true negatives / all truly disease-free
Sensitivity
True positives
The probability of a positive, if the patient really is ill
TP / (TP + FN)
true positives / all truly diseased
Case-control studies are prone to recall bias in general
Cohort studies are prone to selection bias in general
Population attributable risk (PAR)
The portion of the incidence of a disease in the population (exposed and non-exposed) that is due to exposure
It is the incidence of a disease in the population that would be eliminated if the cause of exposure was eliminated
This can be expressed as a value or percentage
Allocative efficiency
Investing in worthwhile interventions
Technical efficiency
Investing in the interventions that make the best use of scarce resources
SPIKES
Setting Perception Invitation Knowledge Empathy Summary
Kubler-Ross model of grief
Denial Anger Bargaining Depression Acceptance
Bowlby model of grief
Numbing
Yearning/searching
Disorganisation
Reorganisation
Most common cancers in men
Lung Bowel Prostate Bladder Stomach
Most common cancers in women
Breast Lung Bowel Bladder Stomach
Most common cancers in children
Leukemia
Brain
Lymphoma
Soft tissue sarcoma
Type I error
False positive
Type II error
False negative
Standardised mortality ratio (SMR)
Ratio between the observed number of deaths (O) in a study population to the number of expected deaths (E)
SMR = O/E
Direct standardisation?
Required we know the age-specific rates of mortality in all populations under study
Indirect standardisation?
Only requires that we know the total number of deaths and the age structure of the study population
When is indirect standardisation preferable?
Small numbers in particular age groups
Likelihood ratio
The likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that the same result would be expected in a patient without the target disorder
Length bias
Overestimation of survival duration among screening-detected cases by the relative excess of slowly progressing cases
Consequences of length bias?
Diseases with a longer sojourn time are ‘easier to catch’ in the screening net.
On average, individuals with disease detected through screening ‘automatically; have a better prognosis than people who present with symptoms/signs.
If we simply compare individuals who choose to by screened with those who don’t we will get a distorted picture.
Lead time bias
Overestimation of survival duration among screen-detected cases (relative to those detected by signs + symptoms) when survival is measured from diagnosis
Consequences of lead time bias?
Survival is inevitably longer following diagnosis through screening because of the ‘extra’ lead time
Because of this the appropriate measure of effectiveness is deaths prevented, not surviva
Over-diagnosis bias?
Overestimation of survival duration among screen-detected cases caused by inclusion of pseudodisease - subclinical disease that would not become overt before the patient dies of other causes.
Occurs when screen-detected cancers are either non-growing or so slow-growing that they never would cause medical problems
Statutes (laws) that oblige doctors to disclose information
Public Health Act 1984
Road Traffic Act 1988
Prevention of terrorism act 1989
3 different types of errors
Knowledge based - Such as forming wrong intentions or plans as a result of inadequate knowledge/experience
Rule based - Encounter relatively familiar problem but apply wrong rule, either misapplication of a good rule or application of a bad rule.
Skills based - Attention slips and memory lapses, involve the unintended deviation of actions from what may have been a good plan. We are all prone to these types of errors, mainly due to interruption and distractions.
Latent error
Develop over time until they combine with other factors or active failures to cause an adverse event
Long lived and often can be identified and removed before they cause an adverse event
What are violations?
Deliberate deviation from some regulated code of practice or procedure
They occur because people intentionally break the rules
List 4 types of violations
Routine - Regularly performed shortcuts due to system, process or task being poorly designed or actions. May become tacitly accepted practice over time
Reasoned - Occasional reasoned deviation from a protocol or procedure which we believe we have good reason for making (e.g. time constraints), may be in patient’s best interests
Reckless - Deliberate deviations from a protocol/code of conduct and include acts where opportunity for harm is foreseeable and ignored, although harm may never be intended
Malicious - Deliberate deviations from a protocol/code of conduct, where the intention is to cause harm
What is a near miss?
A situation in which events arise during clinical care but fail to develop further
Swiss cheese model of accident causation
Although many layers of defence lie between hazards and accidents, there are flaws in each layer that, if aligned, can allow the accident to occur.
Main causes of individual vs system errors?
Individual error - Errors of individuals, blames individual for forgetfulness, inattention or moral weakness
System error - Conditions under which an individual works, tries to build defences to eliminate errors or mitigate their effect
List 3 antenatal screening tests that identify major abnormalities
Alpha fetoprotein - Raised in neural tube defects and some GI abnormalities
Downs test - Alpha fetoprotein and HCG
Ultrasound - Growth check, cardiac abnormalities, diaphragmatic hernia
Neonatal tests
Blood spot test - PKU, cystic fibrosis, sickle cell disease, congenital hypothyroidism
Physical examination
4 types of neglect
Physical neglect
Educational neglect
Emotional neglect
Medical neglect
Which act says 16 year old has full capacity?
The family law reform act 1969
What is Gillick competency?
Child (under 16) can consent to medical treatment if deemed competent by medical professional, without need for parental permission or knowledge
What are the Fraser guidelines?
Doctor can give contraceptive advice and treatment to a person under 16 if she is mature and intelligent, likely to continue to have sex, and if the treatment if in her best interests
Effects of targeting population for prevention?
Large potential benefit to community
Low potential benefit to individual
May be low perceived benefit to individual
Effects of targeting high risk groups for prevention?
Larger potential benefit to individual
Smaller effect on population rate of stroke
Many of the conditions you treat are asymptomatic
May of the treatments have side effects
What did the PROGRESS trial show?
Reducing blood pressure after stroke reduces risk of stroke recurrence
Occupational causes of asthma
Bakers
Welders
Paint sprayers
Laboratory workers
Occupational causes of COPD
Coal mining Agriculture Construction Dock workers Brick making
Simple coal worker’s pneumoconiosis
After around 10 years coal mining, small nodules are present
Shouldn’t cause major impairment in lung function
Some coal workers have symptoms of chronic bronchitis (cough)
Pneumoconiosis
Occupational restrictive lung disease caused by inhalation of dust (coal dust, silica, asbestos)
Silicosis
Occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lung.
It is a type of pneumoconiosis.
2 types of asbestos fibres
Serpentine - Curly, white asbestos (relatively harmless), cleared with mucociliary escalator
Amphiboles - Short, sharp, blue/brown asbestos (have malignant potential)
What are preference sensitive and probability sensitive decisions?
Preference sensitive - The person might feel strongly about the side effects of the treatment
Probability sensitive - Sensitive to changes in the chance of different outcomes
Clinical decision support systems (CDSS) are designed to aid clinician decision making
Computerised
Paper based
Reminder systems
Developed to aid with particular decisions
Examples of CDSS
Reminder systems - Screening, vaccination, testing, medication use
Decision systems (diagnosis and treatment) - Model individual patient data against
epidemiological data
Prescribing - Advice on drug and dosage, highlights potential drug interactions
Condition management - Assists monitoring patients
Equity in financing
Geographic allocation of funding by weighted capitation
Resourcing determined by population weighted by need
What is class equality/inequality in health care?
Evidence of social class equality in the use of primary care and social class inequality in the use of secondary care
What is efficiency?
Target resources to those activities that give the greatest health gain for the money spent as this will maximise population health gain
Informing these choices required estimation of value of what is given up when a patient is treated (opportunity cost) and the value of what is gained in terms of improvements in the health of patients
Fair-innings arguement (1997)
Older people have had a long life already, therefor fairer to divert resources to younger people
Elderly also have a disproportionate share of the available resources allocated to them
Contradictions for the Fair-innings argument?
Treating on the basis of need might mean older people don’t receive lower priority
Years of life saved shouldn’t matter, the quality of life is more important e.g QALYs
Fairness is not the only thing that matters, other things do too e.g equal treatment
Advantages of cohort studies
Good for rare risk factors
Can assess multiple risk factors at once
Disadvantages of cohort studies
Expensive
Time consuming - Risk factor may take decades to cause disease
Confounding factors
Advantages of case-control studies
Good for rare diseases
Good for tracing source of an outbreak
Disadvantages of case-control studies
Recall bias
Inferior to cohort
What should systematic reviews have in their inclusion criteria?
Papers that have not been published (publication bias)
Papers that are not in English
R0
Basic reproduction rate
The average number of individuals directly infected by an infectious case during the
infectious period, in a totally susceptible population (number of secondary cases following introduction of infection)
What factors affect R0?
The rate of contacts in the host population
The probability of infection being transmitted during contact
The duration of infectiousness
Effective reproduction rate (R)
Estimates the average number of secondary cases per infectious case in a population made up of both susceptible and non-susceptible hosts
Equation for effective reproduction rate
R = R0x (x is the fraction of the host population which is susceptible e.g. half population is 0.5)
R>1 - number of cases increases
R<1 - Number of cases decreases, needs to be maintained for elimination
R=1 - Epidemic threshold
Herd immunity equation
H = (R0-1)/ R0
What are some of the free and private travel vaccines available?
Free - Diptheria, polio, tetanus, typhoid, hepatitis A, cholera
Private - Hepatitis B, japanese encephalitis, meningitis, rabies, TB, yellow fever
Define disability
Restriction or lack (resulting from an impairment) of ability to perform an activity in the manner or within the range considered normal for human being
Dual process model
Better model that says we cope w/ grief/bad things by carrying out loss orientated + restoration orientated behaviours
Loss orientated – grief work, braking bonds, denial
Restoration orientated – doing new things new roles + relationships
These 2 processes occur simultaneously through everyday life experiences
What different forms can the stress response take?
- Direct action
- Seeking information
- Doing nothing
- Developing way of coping
Likelihood ratio
The likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that that same result would be expected in a patient without the target disorder.
What is the likelihood ratio for positive test results?
LR+
Chance of testing positive if you have disease/ chance of testing positive if you don’t have disease
What is the LR for negative test results?
LR-
Chance of testing negative if you have disease/ chance of testing negative if you don’t have disease
What is the significance of LR+ and LR-?
The larger the LR+ the greater chance you have disease if your test is positive
The smaller the LR- the less chance you have disease if your test is negative
What is the pre-test probability?
Chances of disease before test = the disease prevalence in your population
Length bias
Screening is best at picking up long-lasting and slowly-progressive conditions rather than rapidly-progressing poor prognostic ones
Overestimation of survival duration among screening-detected cases by the relative excess of slowly progressing cases
Consequences:
Diseases with a longer sojourn time are ‘easier to catch’ in the screening net.
On average, individuals with disease detected through screening ‘automatically; have a better prognosis than people who present with symptoms/signs.
If we simply compare individuals who choose to by screened with those who don’t
we will get a distorted picture.
Lead time bias
Overestimation of survival duration among screen-detected cases (relative to those detected by signs and symptoms) when survival is measured from diagnosis.
Consequences:
Survival is inevitably longer following diagnosis through screening because of the ‘extra’ lead time
Because of this the appropriate measure of effectiveness is deaths prevented, not survival
Overdiagnosis bias?
Overestimation of survival duration among screen-detected cases caused by inclusion of pseudodisease - subclinical disease that would not become overt before the patient dies of other causes.
Occurs when screen-detected cancers are either non-growing or so slow-growing that they never would cause medical problems
How can waiting lists be measured?
Average or median waiting time Average or median wait of those on list Number on the list (size) Proportion waiting more than x days Proportion of those on list waiting more than x days Time to clear list
Identify two potential disadvantages to individuals or to society that may result from the introduction of a screening programme
False positive results leading to anxiety and unnecessary interventions.
Opportunity cost of the programme for NHS (and individual).
Increased diagnostic activity.
How might measuring BMI in school children be used?
Overweight (or underweight) children are identified and parents take appropriate action.
Schools take action to tackle obesity
The importance of obesity is highlighted in the community
NHS and/or Local Authority have information that can be used to plan services to tackle obesity
Local obesity figures and performance can be monitored
What conditions are screened for in newborns?
Congenital hypothyroidism;
Phenylketonuria;
Medium Chain Acetyl Decarboxylase (MCAD);
Hearing problems;
Cystic fibrosis;
Sickle cell disease;
Give five examples of the problems faced by families affected by AIDS in low income countries.
Children as care givers Orphans Psychosocial distress Poverty Lack of schooling Reduced access to health care services Discrimination Child labour and exploitation Sexual exploitation Street children
HIV/AIDS in Africa is changing the pattern of the population structure.
What is the effect of the changes on the age structure and why should it have this effect?
Reduction in the young and middle aged adults rather than children (2 marks)
Infects sexually active people with an approx. 10 year period to death so time to reproduce is not affected (2 marks)
Where in Africa does HIV/AIDS have most impact?
Sub-Saharan
Give two reasons why waiting times may benefit the NHS.
Act as rationing
Makes best use of resources
Give four initiatives taken in the NHS to reduce waiting lists which might come into your discussion.
More doctors/healthcare staff
Day cases
Targets and penalties for missing them
Activity based remuneration for doctors
Activity based remuneration for hospitals
Star ratings
Other service providers (e.g. contracting with private providers; switch to primary care provision)
What was the outcome of the midwives’ act (1902)?
Established normality in childbearing as the midwife’s role - Refer to doctors as soon as abnormality occurs
This ensures equal access to midwives and doctors for childbearing women of all socioeconomic standing
Benefits of institutionalised childbirth?
Standardisation of care
Access to good facilities to support childbirth
Availability of populations of childbearing women and infants for the purposes of
midwifery and obstetric training
Faster access to emergency care
Access of effective obstetric analgesia
Risks of institutionalised childbirth?
Medicalisation Deposonalisation of birth Lack of privacy Inflexibility in labour and birth practices Limitation of resources
What are the legal aspects of ART?
What act is it laid out in?
Human fertilisation and embryology authority act 2008
- Welfare of child needs to be taken into account
- Need for ‘supportive parenting’ hence valuing role of all (hetero and homo) parents
- Sex selection/social selection of embryos is prohibited
Standardised mortality ratio?
Ratio between the observed (O) number of deaths in a study population to the number of expected (E) deaths
SMR = O/E
Why are waiting times important to patients?
The patient’s condition may deteriorate while waiting and in some cases the effectiveness of the proposed treatment may be reduced
Experience of waiting can be extremely distressing in itself
Patient’s family life may be adversely affected by waiting
Patient’s employment circumstances may be adversely affected by waiting
Excessive waiting times may be symptoms of inefficiencies in the healthcare system
and should be addressed as part of good management
Why do we have waiting lists?
There is a limitless demand for health, people can always ‘be more healthy’ which created high demand
Limited resources - Supply of money, staff etc is finite
Theories of NHS waiting lists?
The backlog - Implies a need for occasional emergency injection of funds
Demand management - Waiting acts as a ‘price’ to deter frivolous use
Allows NHS resources to be fully employed - Don’t want lots of spare capacity as this
is a waste
Waiting lists are caused by underfunding and ineffieciency
How can NHS reduce waiting times?
Manage demand - Ensuring each referral represents the most appropriate decision for the care of the individual patient
Manage the queue - Ensuring waiting lists are well managed and patients are called for treatment in appropriate order
Manage capacity - Providing efficient and effective services that meet the level of demand from appropriate referrals
Provide leadership - Ensuring that all parts of the local NHS work together to achieve waiting time improvements in the best interests of patients.
2000-2008 policy ‘targets and terror’
Performance management of Trusts and PCTs based on achievement of target waiting times
Hospitals receive an overall performance score and managers could lose their jobs if targets missed
What was the pros of ‘targets and terror’?
No inpatients waiting longer than 3 months
Outpatients reduces, significant increased expenditure alongside this, however
funding has now remained constant meaning NHS is struggling despite increased demand
What was the cons of ‘targets and terror’?
Sacrifice of professional autonomy - Managers pressurising doctors, may be forced to treat less urgent due to waiting time.
Unmeasured performance sufferers - Things that don’t have a target may suffer.
Adverse behavioural responses e.g. emergency patients waiting in ambulances not emergency rooms, not classed as being in A+E until they are through the doors so
essentially cheating.
Data manipulation and fraud.
Possible criteria for priority on waiting lists?
Clinical urgency Clinical severity Potential health gain Productivity and economic loss Equity waiting e.g. poverty Length of time waiting
Social consequences of deafness?
Social impact - Difficult to have conversations, isolation, intimacy issues, problems at work
Psychological impact - Anger, low confidence, frustration, depression, embarrassment
Practical issues - Doorbells, phones, theatre and cinema, TV, alarms
Rules for whether people can drive with epilepsy?
Group 1 which applies to cars, motorbikes, and most other small vehicles - Need to be seizure free for 12 months
Group 2 which applies to bigger vehicles such as lorries, heavy goods vehicles and other specialised types of vehicle - Unlikely to qualify for group 2 licence, need to be seizure free for 10 years and have not taken epilepsy medicines for 10 years
There are 3 new rules relating to whether people can drive.
They have only had seizures while they sleep
They have only had seizures that do not affect their consciousness
Their doctor changed their dosage or medication, but they have now gone back to
the original dosage or medication
What % of CAMs are covered by the NHS?
10%
Which CAM is most used for MSK problems?
Oestropathy - moving, sketching, massaging muscles and joints.
What does the NICE guidelines state about acupuncture in lower back pain, osteoarthritis, and headaches?
Low back pain - Consider manual therapy, do not offer acupuncture
Osteoarthritis - Manipulation and stretching should be considered as an adjunct to
core treatments, do not offer acupuncture
Headache/migraine - Consider a course of up to 10 sessions of acupuncture over 5-8
weeks
According to the mental capacity act 2005, a person lacks capacity if they are unable to …
Understand information that may be relevant to the decision, including the consequence
Retain information, even for a short time
Use or weigh information to make decisions
Communicate decision
Type 1 error (false positive)
The null hypothesis is REJECTED when it is true
i.e. Showing a difference between two groups when it doesn’t exist, a false positive. This is determined against a preset significance level (termed alpha).
As the significance level is determined in advance the chance of making a type I error is not affected by sample size. It is however increased if the number of end-points are increased. For example if a study has 20 end-points it is likely one of these will be reached, just by chance.
Type 2 error (false negative)
The null hypothesis is ACCEPTED when it is false.
i.e. Failing to spot a difference when one really exists, a false negative.
The probability of making a type II error is termed beta. It is determined by both sample size and alpha
Define risk
Probability of an event in a given time period.
Define risk ratio
Risk ratio = Risk exposed/ Risk unexposed
Risk ratio = Risk of CVD smoker/Risk of CVD non smoker
Cohort studies
Population attributable risk?
The risk of disease will increase as the exposure prevalence or relative risk increases
Main risk factors associated with lung cancer?
Smoking (90%) Radon Asbestos Environmental tobacco exposure Genetics Other lung diseases Prior radiation in chest area
Different types of lung cancer?
Small cell (13%)
Non-small cell (87%)
- Adenocarcinoma (>40%),
- Squamous cell carcinoma (20%),
- Large cell carcinoma (2%)
Mesotheloma
Prevention paradox
A preventive measure that brings large benefits to the community offers little to each participating individual
How are confounding factors limited?
Restriction - Limit the participants of your study who have possible cofounders
Means that you have less data and difficult with multiple confounders
Matching - You create a comparison group that is matched on the possible confounder, make case and control group as similar as possible on the confounder and then ask about exposure status
Used for strong confounders like age and sex
Stratification - Analyse exposure:outcome association in different subgroups of the confounder, recombine data and use a weighted average of the strata
Limitations - To take into account all confounders would require lots of strata and you may run out of data to fill all possible options in your strata
Multiple variable regression - You can adjust for the effects of multiple confounders, try and produce a linear model between the outcome and the different exposures
Allows for adjustment of estimates for confounding
Types of research ethics committees?
NHS Research ethics committees
Higher Education Institution (HEI) research ethics committees
Gene therapy advisory committee
Social care research ethics committee
Ministry of defence research ethics committee
What was the Calman-Hine report?
Examined cancer services in the UK, and proposed a restructuring of cancer services to achieve a more equitable level of access to high levels of expertise throughout the country.
What are the stages in the transtheoretical model?
Precontemplation
- No recognition of need/or interest in change
Contemplation
- Thinking about changing
Preparation
- Planning the change
Action
- Adopt new habits
Maintenance
- Active practice of new healthier behaviour
What is the significance of LR+ and LR-?
The larger the LR+ the greater chance you have disease if your test is positive
The smaller the LR- the less chance you have disease if your test is negative
How can utility be assessed?
QALY
Standard gamble – Assesses utility for a health state by asking how high a risk of death would accept to improve it.
Time-trade off – Utility assessed by asking how much time (life expectancy) would give up to improve it
Risk ratio
Used in cohort studies
Risk in the exposed group DIVIDED BY risk in control group
Odd ratio
Comparing patients who already have the condition with patient who do not.
Used in case controls.
Odds of having being exposed to a risk factor DIVIDED BY odds in the control group
What is restriction?
To manage confounding, limiting participant of study who have possible confounders.
Means you have less data
What is matching?
Creating a comparison group that is matched on possible confounder.
Used for strong confounders like age and sex
What is stratification?
Analyse exposure:outcome association in different subgroups. e.g. CHD in pie eaters v non-pie eaters
5 ways to limit confounding variables?
Restriction Matching Stratification Multiple variable regression Standardisation
What is multiple variable regression?
Adjusting for the effects of multiple confounders, producing a linear model between outcome and different exposures
What is standardisation?
To limit confounding, usually for age.
Comparing 2 groups in age subgroups
What is standardised mortality ratio?
Comparing how many deaths you would expect to how many there actually were.
SMR > 100% = higher death than average.
This is an example of indirect standardisation
Directly standardised rates?
Take a weighted average of stratum specific rates, comparing between 2 groups
Equation for risk ratio
Risk in exposure / Risk in unexposed
RR = a/a+c divided by c/c+d
What is population attributable risk?
Risk of disease will increase as the exposure prevalence or relative risk increases
What is absolute risk reduction?
In general, absolute risk reduction is the difference between one treatment comparison group’s event rate (EER) and another comparison group’s event rate (CER).
The difference is usually calculated with respect to two treatments A and B, with A typically a drug and B a placebo.
ARR = c/(c+d) - a/(a+b)
Pre-test probability is equivalent to the prevalence of a condition
The proportion of people with the target disorder in the population at risk at a specific time (point prevalence) or time interval (period prevalence)
For example, the prevalence of rheumatoid arthritis in the UK is 1%
Which one of the following is the best definition of the p value?
A. The probability of obtaining a similar result, assuming that the null hypothesis is true
B. The probability that a replicating experiment would not yield the same conclusion
C. The probability of obtaining a result at least as extreme, assuming that the null hypothesis is true
D. The probability that the null hypothesis is true
E. The probability of obtaining a result at least as extreme, assuming that the null hypothesis is false
C. The probability of obtaining a result at least as extreme, assuming that the null hypothesis is true
The p value is the probability of obtaining a result by chance at least as extreme as the one that was actually observed, assuming that the null hypothesis is true. It is therefore equal to the chance of making a type I error (see below).
When does a type 2 error occur?
The null hypothesis is ACCEPTED when it is false.
A type II error occurs when the sample size in a study is too small to allow for a difference to be detected.
A type II error can be prevented by recruiting a larger sample size.
When does a type 1 error occur?
The null hypothesis is REJECTED when it is true
A type I error occurs when the investigators conclude that there is a difference in a study when in reality there is none. Investigators usually set an arbitrary value such as 0.01 or 0.05.
This means that the investigators accept that there is a 1% or 5% chance that any difference detected is due to chance.
Lead time bias
A lead-time bias is introduced in a study when a disease is detected an earlier stage and this gives the impression that the survival time from the detection point has increased. In reality, the increase in survival time is because the disease is detected earlier and the time of death remains unchanged.
In the analysis stage of an experiment how can confounding variables be controlled for?
In the analysis stage of an experiment, confounding can be controlled for by stratification.
NOT RANDOMISATION
What systems are in place in the NHS to try and prevent errors occurring?
National Patient Safety Agency (NPSA) - 2001. coordination of reporting and learning from mistakes that affect patient safety.
National Reporting And Learning System (NRLS) - 2004. National system for anonymous reporting of patient safety incidents, including near misses. All trusts now have a local system for reporting, linked to the national system. Also has a E- form for reporting incidents anonymously directly to the NPSA.
Medicines and Healthcare - Products Regulatory Agency (MHRA) - Ensures medicines, healthcare products and medical equipment meet appropriate standards of safety, quality, performance and effectiveness and that they are used safely. Monitoring of medicines and acting on safety concerns. Responsible for adverse incident reporting system for medical devices.
How to know is a hospital is safe?
Hospital mortality data
Data on other measures of safety - Reports of never events and serious incidents,
NHS safety thermometer, patient safety dashboards
Monitoring and inspections by regulators - Care quality commission (CQC), NHS
Improvement
Give examples of clinical decision support systems (CDSS)
- Reminder systems - screening, vaccinations, testing
- Decision systems for dx and tx
- Prescribing - advice on drug/dosage + highlights potential interactions
- Condition management
Effects of computer support on prescribing?
Reduced time to achieve therapeutic stabilisation Reduced risk of toxic drug level Reduced length of hospital stay Increased size of initial dose Increased serum drug concentration No change in adverse effects of drug
Staph aureus infection
Transmission - Contaminated food by skin/nasal flora
Produces enterotoxins
Incubation - 2-4 hours
Symptoms - Rapid onset, projectile vomiting and diarrhoea
Salmonella infection
Transmission - Ingestion of contaminated food, faecal contaminations, person- person, infected animals
Can cause enteric fever or enterocolitis
Incubation period - is 12-72 hours
Symptoms - Vomiting, diarrhoea, fever, headache, chills
Cryptosporidium infection
Transmission - Animal-human, person-person, contaminated water or land, associated with foreign travel
Incubation - 2-5 days
Symptoms - Watery or mucoid diarrhoea, severe illness in immunocompromised
Escherichia coli infection
Transmission - Contaminated food, person-person
Incubation - 1-6 days
Symptoms - Haemorrhagic colitis, 5% get haemolytic uraemic syndrome
What is an outbreak?
Incident in which two or more people, thought to have a common exposure, experience a similar illness or proven infection
What might outliers in an outbreak represent?
Baseline level of illness Outbreak source A case exposed earlier than the others An unrelated case A case exposed later than the others A case with a longer incubation period
How can analytical epidemiological studies be useful to identify probably food source of outbreak?
Compare food history of ill and well persons
Point source outbreak - Cohort study
Common source of outbreak - Case-control study
Main dietary associated with cancer
Oesophageal - Alcohol, obesity
Stomach - Possible salted preserved foods
Pancreas - Overweight, obesity
Hepatic - Aflatoxin contamination
Colorectal - Preserved and red meat, alcohol, body fat
Breast - Alcohol, overweight
Urologic - high calcium
What are the different types of results?
Therapy - Look at relative risk reduction, absolute risk reduction, odds ratio, number needed to treat, confidence intervals
Diagnosis - Look at sensitivity, specificity, positive predictive value, negative predictive value, likelihood ratios
Prognosis - Look at how likely the outcomes are over time and how precise the prognostic estimates are (relative risk or odds ratios)
Harm/aetiology - Look at relative risk, odds ratio, number needed to harm
The National Service Framework on Children and Young People has made suggestions for the improvement of children’s health including accidents.
Give three key messages that the NSF suggests to improve child health.
Tackle health inequalities including poverty
Improving access to services/information
Focus on early intervention/Sure Start
Promote physical mental and emotional wellbeing
Promote healthy lifestyles
Setting standards
Compare the importance of childhood accidents with other causes of child ill health and death.
Accidents are a major cause of death in children
They cause twice as many deaths in children as cancer and leukaemia
Cause 6 times as many childhood deaths as murder (homicide)
The incident rate of childhood accidents has not fallen in recent decades as quickly as, for example, diphtheria and pneumonia
What are the arguments for and against age-based rationing being applied to micro-level resource allocation decisions?
For - Age should be relevant because older people are less likely to respond to treatment and have a poorer prognosis in general due to increased complication risk
Against - Age alone is not a good predictor of prognosis/complications hence need case-by-case decisions, decisions based on age may be hidden form of discrimination
Which act protects discrimination based on age, race, sex, gender, disability, religion etc.?
Equality Act 2010
What do clinical and economic evaluations investigate?
Clinical - efficacy and effectiveness
Economic - efficiency
Advantages of systematic reviews over other research designs for answering clinical questions.
A systematic review is a rigorous summary of all the research evidence that relates to a specific question.(1 mark)
By bringing together all the relevant evidence disadvantages of single studies can be guarded against.(1 mark)
Identify two potential weaknesses of the search strategy used by the authors of the review (for systematic review).
Explain why these features might bias the findings of the review
- They have only looked at publications in English
- They have only searched one database – e.g. Medline
- Relevant publications might be published in non English language journals.
- Not all relevant articles may be indexed in Medline.
- A thorough search will reduce the risk that studies that might influence the results of the review will be missed
- Trial reports that are translated for publication in English language journals tend to have bigger effect sizes (i.e. so English-language only searches tend to overstate the effect of an intervention).
How can consumer protection be improved?
Appraisal by peers
Revalidation by the GMC
Medical audit as a compulsory part of routine practice and annual job planning
GP and consultant contracts - Increasing transparency in comparative performance
in relation to activity, costs, and patient reported outcomes
Transparency and accountability
What does NICE do?
What are the different consumer protection agencies?
What medication is used for secondary prevention of strokes?
Ischaemic - Clipidogrel, statin, anti-hypertensive, anticoagulant if AF
Haemorrhagic - Anti-hypertensives
Which act protects discrimination based on age, race, sex, gender, disability, religion etc.?
Equality Act 2010
What do clinical and economic evaluations investigate?
Clinical - efficacy and effectiveness
Economic - efficiency
What are the different consumer protection agencies?
- CQC (care quality commission)
- NICE ()National Institute for Health and Clinical Excellence
- DoH and NHS England - oversight of cost and quality control
- GMC- regulates medical schools and practitioners
- Royal colleges - examine and certify practitioners
National service framework?
Set national standards and define service models for a service or care group
Put in place programs to support implementation
Establish performance measures against which progress within agreed timescales would be measured
How can consumer protection be improved?
Appraisal by peers
Revalidation by the GMC
Medical audit as a compulsory part of routine practice and annual job planning
GP and consultant contracts - Increasing transparency in comparative performance
in relation to activity, costs, and patient reported outcomes
Transparency and accountability
What does NICE do?
What are the different consumer protection agencies?
What medication is used for secondary prevention of strokes?
Ischaemic - Clipidogrel, statin, anti-hypertensive, anticoagulant if AF
Haemorrhagic - Anti-hypertensives
What is R0 porportionate to?
- The length of time the case remains
- Number of contacts a case has with susceptible hosts per unit time
- The chance of transmitting the infection during an encounter with a susceptible host
