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ESA 1 Revision > HaDPop > Flashcards

HaDPop Flashcards

1
Q

Define a CENSUS

A

The simultaneous recording of demographic data by the government at a particular time, pertaining to all of the people who live in a particular territory.

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2
Q

What are the uses of a census?

A

Population projections and trends (age, ethnicity etc), allocation of resources for health, housing, employment, transport.

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3
Q

Define the Crude Birth Rate (CBR)

A

The number of live births per 1000 population (per year).

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4
Q

Define the General Fertility Rate (GFR)

A

The number of live births per 1000 females aged 15-44 (per year)

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5
Q

Define the Total Period Fertility Rate (TPFR), and how it is calculated.

A

The average number of children that would be born to a hypothetical woman in her lifetime. It is the sum of the current age specific fertility rates. (Short term measure, not long term).

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6
Q

What is the disadvantage of Crude Birth Rate?

A

Men and women who are not of fertile age do not give birth.

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7
Q

Give one advantage of General Fertility Rate and one reason why it might not be calculated.

A

It is more accurate for measuring birth rates as it only describes fertile female populations. However it is difficult to ascertain fertile females in some areas.

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8
Q

What does TPFR account for?

A

Confounding.

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9
Q

Define fecundity

A

Physical ability to reproduce

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10
Q

Define fertility

A

Realisation of the potential of fecundity as births

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11
Q

What affects fecundity?

A

Hysterectomy, sterilisation

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12
Q

What increases fertility?

A

Sexual activity, good economic climate

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13
Q

What decreases fertility?

A

Contraception, abortion

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14
Q

Conceptions =

A

Live births + miscarriages + abortion

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15
Q

Define Crude Death Rate (CDR)

A

Number of deaths per 1000 population per year

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16
Q

Define: Age Specific Death Rate

A

Number of deaths per 1,000 in age group (per year)

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17
Q

Define Standardised Mortality Ratio (SMR)

A

Compares the observed number of deaths with the number of expected if the age-sex distributions of populations were identical. Describes local population to general population.

Takes into account confounders

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18
Q

How do you calculate SMR?

A

observed no. of deaths/ expected no. of deaths x100

SMR of 100 is same as ref population

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19
Q

What does SMR account for?

A

Confounding

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20
Q

What do SMR values above and below 100 suggest?

A

SMR > 100 suggests excess mortality

SMR < 100 suggests less mortality

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21
Q

What is Birth Notification and when and who is it done by?

A

Notification by an attendant at birth (usually a midwife) for relevant services such as immunisation purposes etc. It must be done with 36 hours to local Child Health Registrar.

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22
Q

What is Birth Registration, and when and who is it done by?

A

For statisitical purposes to Local Registrar for Births, by parent, within 42 days.

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23
Q

What is Death Certification?

A

An obligation by an attending doctor to provide the likely cause of death, and notify a coroner if unsure or suspicious.

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24
Q

What is Death Registration?

A

To local Death Registrar, within 5 days by a qualified informant, usually a relative. Requires a Death Certificate.

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25
Q

What is a confounder?

A

Something that is associated with both the outcome and exposure of interest, but is not on the causal pathway between exposure and outcome.

They distort and give misleading results.

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26
Q

Define Incidence rate

A

The number of new cases of a disease, per 100 people per year (person years)

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27
Q

Define prevalence (proportion)

A

The amount of people who currently have a disease in a set population.

Denominator is persons, no time period

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28
Q

Define incidence rate ratio

Calculation?

A

Comparison of the incidence rates in two populations with differing levels of exposure. Relative risk.

IRR = RateB (exposed) / RateA (unexposed)

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29
Q

What is another use of IRR

A

Efficiacy of treatment.

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30
Q

What are some common confounders?

A

Age, sex, ethnicity

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31
Q

What is the difference between systematic and random variation?

A

Systematic: can be attributed to various factors e.g. age.

Random: when fluctuations can not be explained.

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32
Q

What is a confidence interval? (95%)

A

The range in which we can be 95% sure that the true value of the underlying tendency lies.

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33
Q

How do you calculate a confidence interval?

A

Lower bound = value / error factor

Upper bound = value x error factor

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34
Q

How would you carry out a hypothesis test?

A
  1. State the null hypothesis
  2. Work out the IR/IRR
  3. Work out the error factor
  4. Work out the 95% confidence interval
  5. Interpret your data
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35
Q

What is the null hypothesis?

A

There is no difference in risks between exposed and unexposed populations. The IRR is 1, the SMR is 100.

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36
Q

What values of p are statistically significant? (and therefore can reject the null hypothesis)

A

When p<0.05

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37
Q

When p>0.05, what conclusion can be drawn?

A

There is little or no evidence against the null hypothesis, however it is not proven, it can not be accepted.

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38
Q

What is the p value?

A

The probability that the data observed is simply due to chance and of obtaining a test statistic.

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39
Q

What are the limitations of hypothesis tests?

A

Rejecting a hypothesis is not always useful, the 0.05 value of p is arbitrary.

Statistical significance depends on sample size.

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40
Q

What is biasing?

A

The deviation of the results from the truth via certain process

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41
Q

What is selection bias?

Give 2 examples

A

Error due to systematic differences in the ways in which the two groups were collected.

Allocation bias, healthy worker effect

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42
Q

What is information bias?

Give 2 examples

A

Error due to systematic misclassification of subjects in the group

Recall bias, publication bias

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43
Q

What does a cohort study involve?

A

Recruiting disease free individuals and classifying them according to their exposure status.

They are followed up for extended periods, disease progress is monitored and incidence rates are calculated, then IRR.

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44
Q

What are the types of cohort study?

A

Prospective and retrospective.

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45
Q

What is a prospective cohort study?

A

Disease free individuals are recruited in the present and followed up in the future.

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46
Q

What is a retrospective cohort study?

A

DIsease free individuals are recruits, exposure status calculated from historical documentation, and followed up.

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47
Q

What are the two types of comparison?

A

Internal and external

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48
Q

Give 3 problems with internal comparison

A
  • Sub cohorts may be of radically different sizes.
  • Large studies may be needed.
  • Sub cohorts may not be comparable in respect of confounding factors.
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49
Q

What is internal comparison?

A

Comparison between sub-cohorts within the original group, which are exposed and unexposed.

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50
Q

What is external comparison?

A

This occurs when the exposed population is compared against a reference population instead, using an SMR calculation.

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51
Q

Give 4 problems with external comparison

A
  • There is often limited data pertaining to the reference population as you have not collected it.
  • Often no incidence data.
  • Usually have to make do with mortality data.
  • Study and reference populations may not be compatable; selection bias, the healthy worker effect
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52
Q

What is the healthy worker effect?

A

When biasing of results in studies involving occupational cohrts are compared to a reference population.

Employed individuals are more likely to be healthy than an unemployed individual, as you have to be healthy to work.

When comparison is made, it should always be done against other workers in order to prevent bias.

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53
Q

What is sensitivity analysis?

A

A technique used to determine how different values of an independent variable will impact a particular dependent variable under a given set of assumptions

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54
Q

What are the underpinning concepts of HaDPop?

A

Truth

Bias

Confounding

Chance

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55
Q

Why is cancer registered?

A

Every new diagnosis

Tp monitor trends in incidence and prevalence, survival, screening and care quality

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56
Q

Define morbidity:

A

Any departure, subjective or objective, from a state of physiological or psychological well being.

Sickness, illness and morbid condition are similarly defined and synonymous

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57
Q

What areas is morbidity data held on in particular?

A

Cancer

Communicable diseases: 33 to notify

Congenital abnormalities

Abortion: notify cheif medical officer

58
Q

What is population size determined by?

A

Births

Deaths

Migration in and out

59
Q

What are sources of health information?

A

NHS: Hospital Episodes Statistics

GP registrations

Quality and Outcomes Framework

60
Q

What are methodological issues with collecting health information?

A

Completeness/duplications

Accuracy

Variations in disease diagnosis over time

Numerator/denominator mismatch

Indirect nature of data

Confidentiality

Record Linkage

61
Q

What can a low response rate to a study cause?

A

Non responder bias, innacurate representation of true value

62
Q

What does prevalence equal?

A

Incidence x Mean Disease Duration

63
Q

What is incidence rate a good measure of?

Give a specific type of incidence rate

A

Determines epidemics, effects of prevention programmes, good for short term illness, can compare risks between populations

Mortality rate

64
Q

What is prevalence a good measure of?

A

Incurable, long standing diseases

How many people need to be cared for at a particular moment in time, services needed

65
Q

What is the relationship between incidence and prevalence?

A

All prevalent cases were once incident

Higher incidence=higher prevalence

Prevalent cases always added to by incident cases

Prevalent cases depleted by death or recovery

New treatment which prolongs life = increased prevalence

More cured/death = decreased prevalence

66
Q

Why is systematic variation useful?

A

It gives us clues about the aetiology (cause) of disease

Can compare levels of exposure in two groups to identify cause, prevent exposure and reduce incidence

67
Q

What is variation?

What is the difference between systematic and random variation

A

Difference between observed and actual value

Systematic can be attributed to particular factors such as age

Random when fluctuations can not be explained

68
Q

What is a hypothesis?

A

A statement that an underlying tendency of scientific interest takes a particular quantitative value

69
Q

What is a hypothesis test?

A

Calculation of the probability of getting an observation as extreme as, or more extreme than the one observed, assuming the stated hypothesis is true

70
Q

What are the limitations of the p value?

A

Rejecting a hypothesis is not always useful

0.05 value is arbitrary

Statistical significance depends on sample size, does not always correlate to clinical importance

71
Q

Where does the observe value lie in a 95% confidence interval?

A

In the middle

72
Q

How should a cohort study analysis be done?

A

Null hypothesis

Calculate IRR

Calculate error factor

Confidence interval

Conclusion

73
Q

How to write a conclusion for a test analysis

A

Sufficient evidence to reject null hypothesis? Yes/No

Explain with reference to confidence interval

Statistically significant? Yes/no, give p value

Explain how many times likely to develop disease

74
Q

Define person years

A

The sum of the total time of everybody followed up in a study

No of people exposed x time exposed for

75
Q

What are advantages of cohort studies?

A

Can study exposures and personal characteristics that are not routinely collected

Good for rare exposures

Opportunity to look for different potential outcomes at once from varying exposures

Obtain detailed info on outcomes and exposures

Collect additional data on potential confounders, can adjust

Establish that exposures precede outcomes

Specific calculation of absolute risk

76
Q

What are disadvantages of cohort studies?

A

Large, resource intensive, expensive

Take a long time (historical less), ethics

Rigorous definitions of disease can require expensive and invasive investigatio

Risk of high number of losses to follow up - survivor bias

Not good for rare diseases - too few cases

Diffculty with unknown confounders

77
Q

What is a case control study?

A

Recruit disease free individuals (controls)

Recruit diseased individuals (cases)

Then determine their exposure status

Compare level of exposure in both

Analyse by calculating an odds ratio

Generally retrospective

78
Q

How is an odds ratio calculated?

A

AD/BC

Odds being exposed of cases/odds being exposed controls

Table with cases and controls on top

Exposed and unexposed down side

79
Q

How many controls should be used?

A

4 to 6 times the number of cases

As precision of OR affected by total number of controls as well as cases

Decreases the error factor

80
Q

What isa nested case control?

A

Case control within a cohort

Good as can calculate IR

Population for sampling controls already defined

Need detailed info only on a few individuals

81
Q

What are the issues with a case control study?

A

Selection bias: cases should be representative of all cases, not just in specialist centres

Information bias: recall bias, exposure status incorrectly determined. Different questionnaires, random inaccurate measurement

82
Q

How can confounding be minimised in a case control study?

A

Match cases and controls using important confoundeds (age, sex, dates of birth)

Adjusted with analysis using logistic regression

83
Q

Describe advantages of case control studies

A

Good for rare diseases

Can look for different potential exposures at once

Quicker so cheaper than cohort studies

84
Q

Describe disadvantages of case control studies

A

Can’t obbtain absolute risks (unless nested)

Heavily affected by selection and recall bias

Not good for rare exposures

85
Q

In terms of Henle Koch postulates, what 3 things must a cause be?

A

Agent must be present in every case of the disease

A cause always precedes the disease (NECESSARY)

Cause is absent in other diseases (SPECIFIC)

A cause alone can lead to the disease, can be recovered from experiemental inoculated animals (SUFFICIENT)

86
Q

Give examples of causes and diseases which are necessary, sufficient, both or neither

A

Necessary, not sufficient: TB and mycobacterium TB

Sufficient, not necessary: Lung cancer and radon gas

Necessary and sufficient: measles and the measles virus

Neither necessary or sufficient: TB and poor living conditions

87
Q

What does disease result from?

A

An interplay of host, environment and agent

88
Q

Define a cause

Why is it important to identify causes?

A

An exposure or factor that increases the probability of disease

They do not have to be necessary or sufficient to be importnat causes

Aim is to use the knowledge gained to remove, avoid, or protect against harmful factors

89
Q

What can apparent associations be caused by?

A

Chance, p value measure this

Bias, selection or information

Confounding, known or unknown

Due to common cause

Reverse causailty

Could be true causal association

90
Q

What are the bradford hill criteria?

A

Strenght of association

Specificity of association

Consistency of association

Temporal Sequence

Dose response

Reversibility

Biological plausibility

Analogy

Cohernece of theory

91
Q

How is an RCT carried out?

A

Identify eligible patients

Invite

Allocate treatment randomly

Follow up identically

Minmise losses to follow up, maximise compliance

Analyse date, obtain results

92
Q

Why is a non random trial weak?

A

Selection bias, by patient, clinician or investigator

Confounding

93
Q

What is the advantage of randomisation in a trial?

A

Minimal allocation bias

Minimal confounding, similar size groups and characteristics by chance

94
Q

Why might differences between groups occur in an RCT?

A

Knowledge of which patient is receiving which treatment

Patient may change behaviour/expectations

Clinician may make different secondary care choices

95
Q

What does blinding do in an RCT?

A

Knowledge of treatment allocation not available

Can be single (patient)

Or double (patient and clinician)

Ideally investigator too

96
Q

Why is it important ot blind clinicians in an RCT?

A

Doctors more likely to place healthier patietns in new drug group

Show more postive results

For statistically significant results

97
Q

What is it difficult to blind for in an RCT?

A

Surgery

Psychotherapy vs anti depressant

Alternative medicine vs western medicine

Lifestyle interventions

Prevention programmes

98
Q

What is a placebo?

A

An inert substance made to appear identiceal in ever way to the active formulation to which it is being compared

99
Q

What is the aim of a placebo?

A

To cancel out any placebo effect that may exist in the active treatment

100
Q

What is the placebo effect?

A

The psychological effect/benefit that derives from being looked after more carefully or differently, or from being on a new special treatment

Can result in improvement of clinical condition due to making you feel better psychologically

101
Q

What are the ethical issues of using a placebo?

A

Should only use when no standard treatment is available

Form of deception

Essential that all participants are informed that they may receive a placebo

102
Q

What is a primary outcome?

What is a secondary outcome?

A

Primary: preferably only one, used in sample size calculations

Secondary: other outcomes of interest, often side effects, can be promoted wrongly when statistically significant

103
Q

What are outcome types?

A

Pathophysiological - objective

Clinically defined

Patient focused - subjective

104
Q

What do RCTs measure?

A

Efficacy and harm of treatments

105
Q

How should trials be analysed?

A

Intention to reat: non compliers included in results to give an idea of how the drug would do in real life clinical practice. Preserves randomisation

As treated only compares physiological effects, may miss side effects, loses randomisation

106
Q

How can losses be minimised and compliance maximised in a clinical trial?

A

Follow up appointments at practical times

No coercion or inducements

Honesty to patient

Simplify instructions

Let patient ask Qs

Cool off period

Make simple and accessible to patients

Measure compliance with blood/urine tests

107
Q

Describe RCT ethics

A

Clinical equipoise: reasoble uncertainty on which drug is better for the patient, so not subjecting patients to a known less effective treatment or known harm (loss of autonomy compensated by greater monitoring, care and placebo)

Scientificially robust: address relevant valid issue of benefit, pursuit of knowledge for the good of the population. Appropriate study design and protocol, large enough to find clinical importance, stop if harmful

Ethical recruitment: no inclusion of participants in region unlikely to benefit (e.g AIDS), or those witha high risk of harm , no innapropriate exclusion of those who are not in ideal homogenous group, those with co morbidites, elderly, children

Valid consent and voluntariness: no coercion, knowledgable informant,cooling off period.

108
Q

What are the 4 principles with any medical role?

A

Principle of

Benefiance (do good)

Non-Malefiance (do no harm)

Autonomy (let the patient decide)

Justice (Be fair)

109
Q

What must be the primary consideration of a research study according to a research ethics committee?

A

Dignity, rights, safety and well being of participants

Focus of design, conduct, recruitment, care, confidentiality, consent, benefits after study

110
Q

What is stratified random sampling?

A

Random but selecting certain age groups

111
Q

What is a cross over trial?

A

Both arms of the study get both interventions

112
Q

What is study contamination?

A

Patients in the other control group are subject to the new intervention

113
Q

What is a sample size calculation?

A

FOr a good study, tels us what the calculation is based on

e.g. a 10%different in outcome,and what size study they need as a result

114
Q

What is the difference between bias and confounding?

A

Bias is any deviation of results from the true value, or processes leading to this, due to something systematically wrong with the study.Feature of study being conducted, different samples or treated differently, selection and information bias. Does not correctly reflect population it purports to measure.

Confoudning gives rise to a spurious assoication because of another causal factor, which is due to the structure of the population being studied.Feature of population, influences measure of association, can lead to misinterpretation. Something associated with both the outcome and exposure of interest, but is not on the causal pathway between exposure and outcome

115
Q

What are the limitations of using evidence from individual studies?

A

Can’t read all individual studies

Statistical significance may be due to chance

Different types of study have different weaknesses

On trial can’t definitively answer a hypothesis

116
Q

What are the weaknesses of expert reviews?

A

They make implicit assumptions

Opaque methodology

Biased

Subjective

Not reproducible

117
Q

What qualities should studies used in systematic review be?

A

Transparent

Reproducible

Explicit

118
Q

What is a systematic review?

A

An overview of primary studies that use explicit and reporducible methods

Usually RCT - maybe cohort or case control

Large amount of studies initially identified then narrowed down to most reliable and credible

119
Q

What is a meta analysis?

A

Wtihin a systematic review, used to provide quantitative analysis of the primary studies’ results (that addressed the same hypothesis in the same way)

Proveds an overall value with associated confidence intervals (estimate of the true value)

Can show results via a forest plot

120
Q

What is the purpose of a meta analysis?

A

Facilitate synthesis of many studies

Systematically collate study results

Reduce problems in interpretationdue to variations in sampling

Quantify effect sizes and their uncertainty as a pooled estimate

Sits within a systematic review

121
Q

How is a forest plot interpreted?

A

ORs and CIs combined to give a pooled estimate

Studies weighted according to size and OR certainty (ef size)

Squares give ORs, lines give CIs for each study

Size of square proportional to weight given

Solid line = null hypothesis

Diamond is the pooled estimate with its width the 95% CI

122
Q

Ideally, what should studies in a systematic review be?

A

Homogenous: similar in terms of study design, participant profile, treatments/exposures, oucomes measured, statisitcal analysis used

Though in practice no two studies are identical

Usually heterogeneous

123
Q

What are the two models used to show meta analysis?

A

Fixed effects model

Random effects model

Point estimate (OR) is usually similar

Often both methods are used

124
Q

What is the fixed effects model?

A

Assumes the studies used are homogenous and any variation between data comes from within study variation

Estimating the same effect size

ONE TRUE EFFECT

Weight by study size

125
Q

What is the random effects model?

A

Assumes the studies are heterogenous

Estimating similar, not same effect size, range of true effects which average to a mean value

Variation in data from within study and between study variation

Gives more weight to smaller studies, used when large variance between studies, more equal weights

95% CI usually wider

126
Q

How is heterogeniety tested for?

A

Hypothesis test for heterogeneity

Weak test, low statistical power

Often at 10% significance level

127
Q

How can heterogeniety be explained?

A

Sub group analysis

Stratification

by study characteristics

by participant profile

128
Q

How is quality assessed in a systematic review?

A

Basic quality standard, cochrane only uses RCTs

Score quality, used to weight studies

Sub group analysis

Meta regression analysis

More than one assessor to handle disagreements

Can try and blind assesors, stops favoruitism, but difficult

129
Q

List study types in increasing order of how prone to bias they are

A

RCTs

non RCTs

Cohort studies

Case control

130
Q

What is publication bias?

A

Studies are only likely to be published if results are

statistically significant

or have a large sample size

If systematic reviews only include published studies, results will be biased

Towards demonstration of effect

131
Q

What are systematic reviews reliant on?

A

Quality of primary studies - garbage in, garbage out

Publication bias, should use both published and unpublished studies

132
Q

How can publication bias be determined?

A

Funnel pot

Check metaanalysis protocol for searching

133
Q

How is a funnel plot interpreted?

A

WEll balanced systematic review will show a funnel shape in its studies when plotted

Biased systematic review will vary in shape

Plot of size of effect (OR) on x axis, vs size of study (1/ef) on y axis

Smaller studies vary from the centre more

134
Q

What are advantages of a systematic review?

A

Explicit methods reduce bias and exclusion of poor quality studies

Mata analysis provides overall figure for studies, and statistical significance

Large amounts of information can be assimilated quickly by healthcare professionals

Reduction in time between research discovery and implementation of clinical use

Used in evidence based practice guidelines

135
Q

What is risk difference vs risk ratio?

A

Risk difference: continuous outcome: e.g. systolic blood pressure
. Not mortality which is one of two outcomes, reduction or increase, - numbers. Null hypothesis is 0.

Risk ratio: compared to null hypothesis of 1.

136
Q

What is a representative sample?

A

When measuring something about a large population, but would be expensive and impractical

Take a sample with representative characteristics

137
Q

What is a random sample?

A

Not intended to be representative of the population

Everyone has an equal chance of selection

138
Q

Random selection vs random allocation

A

Seleciton: recruitment in a clinical trial, affects external validity, e.g. generalisability

Allocation: allocation between treatment groups in a trial, affects internal validity e.g. fair comparison

139
Q

Crude vs standardised

A

Crude: describes what was measure, unadjusted

Standardised: what would be measured if the groups were identical in respect to variables being adjusted for

140
Q

As treated vs intention to treat

A

As treated: what the trial participants did, asses physiological effects of treatments studied

Intention to treat: analysis according to original allocation, preserves randomisation, reflects what would happen in practice

141
Q
A

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