GENERIC + STATS Flashcards
What is a risk ratio?
Aka relative risk
The risk of developing a disease associated with an exposure compared to the risk of developing the disease in the abscence of an exposure
Risk of disease in exposed/ risk in unexposed
How do you interpret risk ratios?
Risk ratio of 1 = identical risk among the 2 groups
Risk ratio >1 indicates an increased risk of the group
Risk ratio <1 indicates a decreased risk for the group
What is a rate ratio?
It compares the incidence rates, person-time rates, or mortality rates of two groups
Rate for group of primary interest / rate for comparison group
How do you interpret rate ratios?
The interpretation of the value of a rate ratio is similar to that of the risk ratio. That is, a rate ratio of 1.0 indicates equal rates in the two groups, a rate ratio greater than 1.0 indicates an increased risk for the group in the numerator, and a rate ratio less than 1.0 indicates a decreased risk for the group in the numerator.
E.g. if rate ratio was 2.2 then people who smoke are 2.2 times more likely to get lung cancer than nonsmokers
Whats the difference between risk and rate?
Risk is the number of new cases that occur during a specified time period divided by a population at risk of becoming a case.
Rate is the number of new cases that occur per the total amount of time a person is at risk of becoming a case.
What is an odds ratio?
a statistic that quantifies the strength of the association between two events, A and B.
The odds ratio is defined as the ratio of the odds of A in the presence of B and the odds of A in the absence of B, or equivalently, the ratio of the odds of B in the presence of A and the odds of B in the absence of A. Two events are independent if and only if the OR equals 1, i.e., the odds of one event are the same in either the presence or absence of the other event. If the OR is greater than 1, then A and B are associated (correlated) in the sense that, compared to the absence of B, the presence of B raises the odds of A, and symmetrically the presence of A raises the odds of B. Conversely, if the OR is less than 1, then A and B are negatively correlated, and the presence of one event reduces the odds of the other event.
How do you calculate odds ratio?
Odds that a case was exposed / odds that a control was exposed
E,.g. Odds of lung cancer in smokers / odds of lung cancer in non-smokers
What is risk difference?
Aka attributable risk
The difference between the risk of an outcome in the exposed group and the unexposed group.
Incidence in exposed - incidence in unexposed
How do you calculate absolute risk?
the number of events (good or bad) in a treated (exposed) or control (non-exposed) group, divided by the number of people in that group
What is the inverse of absolute risk reduction?
Number needed to treat
What is the inverse of absolute risk increase
Number needed to harm
What is number needed to treat?
The number of people with a specified condition who need to be treated for a specified period of time in order to prevent one adverse or beneficial outcome (depending on if its NNT to harm or to benefit)
(Remember this is always a whole number!!)
How do you calculate absolute risk reduction?
The AR of events in the control group rate of disease in unexposed group - the rate of disease in the exposed group
Whats the difference between relative and absolute risk?
Absolute risk refers to the actual probability of an outcome occurring in a specific group regardless of any other factors. I.e. the risk of disease among the population. Being studies
Relative risk on the other hand, compares the risk of an outcome between exposed and unexposed groups.
what is primary prevention?
intervening before health effects occur, through. measures such as vaccinations, altering risky behaviors (poor eating. habits, tobacco use), and banning substances known to be associated. with a disease or health condition
I.e. identifying modifiable risk factors
what is secondary prevention?
Systematically detecting the early stages of disease and intervening before full symptoms develop – for example, prescribing statins to reduce cholesterol and taking measures to reduce high blood pressure.
What is screening?
The systematic application of a test to identify individuals at sufficient risk of a specific disorder to warrant further investigation or direct preventive action, amongst persons who have not sought medical attention on account of symptoms of that disorder.
What are the principles of screening?
the condition should be an important health problem
there should be a recognisable latent or early symptomatic stage
the natural history of the condition, including development from latent to declared disease, should be adequately understood
there should be an accepted treatment for patients with recognised disease
there should be a suitable test or examination that has a high level of accuracy
the test should be acceptable to the population
there should be an agreed policy on whom to treat as patients
facilities for diagnosis and treatment should be available
the cost of screening (including diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible expenditure on medical care as a whole
screening should be a continuing process and not a ‘once and for all’ project.
What are the pros and cons of screening?
Pros - better prognosis, reassurance of a normal test, cost effective, may require less long term therapy
Cons - discomfort of tests, false reassurance of a false negatives, true positives and negatives, overdiagnosis (waste of resources, iatrogenic harm and stress), ethical issues, opportunity cost
What is opportunistic screening>
Opportunistic screening happens when someone asks their doctor or health professional for a check or test, or a check or test is offered by a doctor or health professional. Unlike organised screening which is managed by a national health service to ensure everyone has an equal opportunity to participate and ensure that if the test results are abnormal, the pt receives the correct further testing/management/support.
What is population screening?
A nationally delivered, proactive screening programme which aims to improve health outcomes in people with the condition being screened for, and/or offer information to enable informed choices. It is offered to a group of people identified from the whole population, and defined demographically such as by age or sex.
What is targeted screening?
A nationally delivered proactive screening programme which aims to improve health outcomes in people with the condition being screened for, among groups of people identified as being at elevated/above average risk of a specific condition. Compared to the general population, the target population may be at higher risk because of lifestyle factors, genetic variants or having another health condition.
Targeted screening differs from population screening as it aims to systematically offer screening to more specific groups of people with a higher risk of a condition. For example, age and sex are factors in the risk of lung cancer, but individuals who smoke are at even higher risk.
What is stratified screening?
A nationally delivered, proactive screening programme, offering testing which varies in frequency and modality, according to the level of individual risk. This is designed to achieve a more favourable balance of benefits and harms at individual as well as population level.
Stratification is used in both targeted and population screening programmes, at the point of invitation as well as along the pathway. For example:
people with a family history of breast cancer can be identified and screened more often depending on their level of risk
What is sensitivity and how do you calculate it?
The proportion of patients with disease who get a positive test
True positives / all with disease
TP / (TP+FN)
What is specificity and how do you calculate it?
Proportion of patients without the disease who get a negative test
True negatives / all those without disease
TN/ (TN+FP)
What is a positive predictive value and how do you calculate it?
The post-test probability that pt with a positive test result has the condition
True positives / all those test [positive
TP/(TP+FP)
What is a negative predictive value and how do you calculate it?
The post-test probability that pt with a negative test result does not have the condition
True negatives / all those who test negative
TN/TN+FN
How does prevalence affect sensitivity and specificity?
They remain constant as the test itself doesnt change
How does prevalence affect positive and negative predictive values?
As prevalence rises NPV falls and PPV rises
How does prevalence affect likelihood ratios?
As they rely on sensitivity and specificity
It doesn’t change with prevalence
What is a 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.
Positive LR - how much more likely the person is to receive a positive result
Negative LR - how much more likely the person is to receive a negative result
How do you calculate a likelihood ratio for a positive test result?
Chance of a positive test if disease is present / chance of a positive test if disease is absent
Sensitivity / (1- specificity)
How do you calculate a likelihood ratio for a negative test result?
Chance of a negative test if disease is present / chance of a negative test if disease is absent
(1- sensitivity) / specificity
Whats the difference between odds and risk?
Odds is a ratio of the number of people who develop an outcome to the number of people who dont. E.g. odds of rolling a 4 on a dice is 20% 1:5
Risk is the ratio of the number of people who develop an outcome to the total number of people e.g. 1:6 which is 16.6%
What is a hazard ratio?
A measure of how often a particular event happens in one group compared to how often it happens in another group, over time.
What is a null hypothesis?
the hypothesis that there is no significant difference between specified populations, any observed difference being due to sampling or experimental error.
What is a p value?
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
What is a 95% confidence interval?
A range of values that is 95% likely to contain the true value
What is a type 1 error?
Rejecting the null hypothesis when it is true (false positive)
What is a type 2 error?
Accepting the null hypothesis when it is false e.g. false negativbe
Healthy and unhealthy adjustment responses to physical symptoms, and the impact of personal family and cultural influences
Healthy - seeking medical attention, self-care, seeking social support, developing coping strategies
Unhealthy - substance misuse, denial, avoidance, catastrophizing
Family - those with supportive families are more likely to adhere to medical treatments, engage in healthy behaviours and have a more positive outlook on their recovery. Criticism amd negalect from family can lead to more stress and poorer health outcomes
Culture - some cultures may see it as a punishment, some cultures may encourage natural remedies and holistic approaches to healing
Whats the impact of MUS on life?
the need to feel understood
struggling with isolation
‘sense of self’ in strain
facing uncertainty
searching for explanations
ambivalence about diagnosis
disappointed by healthcare
Feel as though they can’t fully adopt the sick role
What is a post-mortem examination? What contributions can it make to understanding and influencing care of the living?
Also known as an autopsy, is the examination of a body after death, carried out by a pathologist. The aim of a post-mortem is to determine the cause of death.
They angle pathologists to obtain a better understanding of how diseases spread and the pathophysiology of diseases which allows more effective treatment in the future
In thr past they help provide a foundation for understanding the brain e.g. Broca and Wernicke used it, improved medical knowledge and helps generate hypothesis for further study
What are the legal requirements for a coroner’s post-mortem?
In accordance with the Human Tissue Act 2004, consent is needed in order for a hospital post-mortem to take place, either from the patient before death, or from the appropriate next of kin.
Where a coroner deems a post-mortem examination necessary as part of their investigation into the patient’s death, consent is not needed. Where a patient or their next of kin object to a post-mortem, the coroner will take this into account but can, even in the face of this objection, proceed to a post-mortem if they consider that it is necessary.
The coroner may, however, agree to a limited post-mortem in some cases, if this is appropriate and provides the necessary information. In rare circumstances, the coroner may agree to an MRI scan of the body being performed as an alternative to a post-mortem.
What are the legal issues surrounding a post mortem examination?
Coroners and justice Act 2009:
a. A post mortem examination can be authorised by the coroner.
b. The choice of pathologist is to be made by the coroner but, in cases of suspected homicide, he must consult the police.
d. The pathologist undertaking the examination must preserve, as far as possible, all material which bears upon the cause of death or the identification of the deceased.
e. The pathologist must notify the coroner of the material being retained and the reason for the retention.
f. The coroner must notify the pathologist of the period for which the material may be retained.
h. The coroner must notify the next-of-kin of the retention of material and seek their views as to the appropriate treatment for the material when it is no longer required for his purposes.
Human Tissue Act 2004
post mortem examination must take place on premises covered by a licence from the Human Tissue Authority.
A licence in relation to post mortem examination also covers the removal of relevant material for the purposes of the examination; removal for other purposes (e.g. research) would require a separate licence.
The pathologist undertaking the post mortem examination must act under the authority of a licence from the Human Tissue Authority authorising post mortem examinations on those premises.
Samples may only be taken for the purpose of determining the cause of death if the post mortem has been authorised by the coroner.
The performance of the post mortem examination must be in accordance with the Codes of Practice and other guidance, information and advice issued by the Human Tissue Authority
What are the ethical issues surrounding a post mortem examination?
respect for the dead body
retaining tissues from the body for study
the applicability autopsy information has when examining the quality of care provided by a medical institution.
What is the biopsychosocial model of health and illness?
Suggests that to understand a person’s medical condition it is not simply the biological factors to consider, but also the psychological (thoughts, emotions, behaviours) and social factors (socio-economic, socio-environmental, cultural)
What examples can you give of the impacts of chronic ill health has had on psychological processes?
1/3rd of pt with chronic ill health experiences symptoms of depression
Learning to deal with and make sense of distressing sympotms
Learning to cope with new healthcare environments/procedures
Comping with impact of symptoms on own physical/emotional healthy, family roles, work, finances
Grieving for the loss of previous health
No clear diagnosis can make adjustment more challenging and symptoms may be unpredictable
Stress and anxiety can exacerbate physical symptoms
What is a coping style?
the cognitive and behavioural changes that result from the management of an individual’s specific external/internal stressors
What are the 3 types of coping styles?
Problem-focused coping
Emotion focused coping
Avoidance coping
What is problem-focused coping?
a problem-solving technique in which an individual addresses a problem or stressor directly in an attempt to alleviate or eliminate it. It is also referred to as problem-centered coping. For example, a student who is nervous about giving a presentation at a research event may cope by practicing the presentation each night before the event, attending seminars on how to give presentations, or asking friends to listen to the presentation in order to provide feedback to make sure they are fully prepared for the event.
(Considered to be the most effective coping strategy as it’s associated with lower stress levels)
What is emotion0-focused coping?
Emotion-focused coping involves regulating your feelings and emotional response to the problem instead of addressing the problem e.g. mindfulness meditation or journaling
What is avoidance coping?
cognitive and behavioral efforts oriented toward denying, minimizing, or otherwise avoiding dealing directly with stressful demands e.g. procrastination
What act means patients are legally allowed to request to see their medical records?
The Data Protection Act 1988
What is a prevalence ratio?
The prevalence in the exposed group vs the prevalence in the non-exposed group
E.g. a prevalence ratio of 5 indicates that the proportion of the disease is 5 times greater amongst the exposed group than the non-exposed group
What is proportional mortality?
a measure of the percentage of deaths in a specified population that are attributable to a particular cause. It is calculated by dividing the number of deaths due to a specific cause by the total number of deaths in the population, and then multiplying the result by 100.
What is measurement bias?
Where information collected within a Study is not accurate due to an error in data collection during measurement
It’s a systemic bias so is retained across the data set
How do meta-analysis and systematic review differ?
A meta analysis synthesises and combines multiple pieces of pre-existing research in order to investigate a specific topic. Statistical methods are then used to collectively analyse the results and reach a statistically powerful conclusion.
A systemic review is similar but instead answers a specific question purely through synthesis ans summary of a variety of pre-existing studies, without the use of statistically analysis.
What is sampling bias?
The selection of participants for analysis in such a way that proper randomisation is not achieved, thereby ensuring that the sample obtained is not representative of the population intended to be analysed
Which measure of association is best for cross sectional studies?
Odds ratio or prevalence ratio
Which measure of association is best for a cohort study?
Relative risk or rate ratio
What is attrition bias?
A type of selection bias due to systemic differences between study groups due to loss of members during study conduct i.e. loss of participants
How can you reduce attrition bias?
Intention to treat analysos
What is power?
The ability to correctly reject a null hypothesis that is indeed false