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ESA1 > HaDPop > Flashcards

HaDPop Flashcards

0
Q

What are the main features of a census?

A

Run by government
Simultaneous
Universal coverage
Occurs at regular intervals

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1
Q

What is a census?

A

A simultaneous recording of demographic data by the govt at a particular time, pertaining to all the people living in a particular territory.

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2
Q

What are censuses used for?

A

1) . Allow allocation of resources
2) . So we can make projections on populations
3) . Work out trends in populations

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3
Q

What is crude birth rate?

A

The number of live births per 1000 of the population.

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4
Q

What does crude birth rate give us?

A

It gives us the impact of births on the population size.

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5
Q

What is general fertility rate?

A

The number of live births per 1000 females of ages 15-44.

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6
Q

What does GFR compare and how is it affected?

A

It compares fertility of fertile female populations and is affected by age distribution.

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7
Q

What is total [period] fertility rate?

A

The average number of children that would be born to a hypothetical woman in her lifetime.

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8
Q

What does TPFR compare and how?

A

It compares the fertile females fertility without being influenced by age structure, by giving each age group equal weighting in its calculation.

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9
Q

What is the calculation for TPFR?

A

TPFR = sum of (all age specific fertility rates)

e.g. If 24 15yr olds have 6 babies = 6/24 = 0.25

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10
Q

What is fecundity and what affects it?

A

The ability of a population to reproduce.

Affected by sterilisations and hysterectomies.

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11
Q

What is fertility and what affects it?

A

It is the recognition of fecundity as a potential for live births.
Affected by sexual activity, the economic climate, abortion and availability of contraception.

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12
Q

What is crude death rate?

A

The number of deaths per 1000 of the population.

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13
Q

What is age specific death rate?

A

The number of deaths per 1000 in a particular age group.

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14
Q

What is the standardised mortality rate calculation?

A

Number of observed deaths in study pop
——————————————— x 100
Number of expected deaths in study pop

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15
Q

What is standardised mortality ratio and what is its purpose?

A

A comparison of the observed deaths with the number of deaths expected if 2 populations had the same age-sex distribution.
It adjusts for age-sex confounding by comparing a population with a standard reference.

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16
Q

How do you calculate person years?

A

It is the sum of total years exposed per person. e.g. 1 person for 10 years, 3 people for 0.1 years
= (1x10) + (3x0.1)

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17
Q

What is a population estimate?

A

Applying birth rates, death rates and migration to the present.

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18
Q

What is a population projection?

A

Applying birth rates, death rates and migration to make predictions about the future along with additional assumptions.

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19
Q

What is incidence and its units?

A

Units are rate

Incidence is the amount of new cases of a disease in a population in a time.

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20
Q

How do you calculate incidence rate?

A

new events
IR = ————————————
persons x time (years)

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21
Q

What are incidence measurements useful for?

A

Monitoring epidemics.

Giving a measure of the populations average risk of disease (although people vary)

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22
Q

What is prevalence and its units?

A

The number of existing cases in a population

~ (incidence x length of disease)

Unit is a proportion (no. cases/population) = no time element.

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23
Q

When can variation aid a study?

A

1) . Systematic variation can give us clues about the cause of a disease e.g. Exposure levels between 2 groups can be used in studies.
2) . IRR allows us to compare groups.

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24
Q

How do you calculate IRR and what is it useful for?

A

Rate of exposed
IRR = ———————–
Rate of unexposed

It allows us to compare incidence of disease between 2 groups or to compare the efficacy of two treatments.

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25
Q

Why does IRR only give us relative risk?

A

The value it gives us is comparison between 2 groups only (risk of developing the disease n exposed group compared to the risk in the 2nd group, which I selected). This means it isn’t taking into account the general population, and the 2 groups may be systematically different from these.

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26
Q

Why does IR provide absolute risk?

A

Because it compares the number of new events to the general population

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27
Q

When is variation a nuisance?

A

Confounding can explain all/part of an apparent association.

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28
Q

How do you eliminate age-sex confounding?

A

Age-sex confounding always needs to be eliminated.
Use the SMR (compares number of observed deaths to a reference population like the one being studied)
Could use age specific rates but this would be very time consuming as you would obtain many different values.

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29
Q

When is a p value statistically significant?

A

When p<0.05

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30
Q

What are the limitations of the p value?

A

1) . The values p=0.049 and 0.051 are very close together = is there really that much difference?
2) . The statistical significance needs to have a big enough sample size to start with or chance can’t be down to 0.05 (e.g. Flipping a coin).
3) . Statistical significance does not necessarily mean clinical importance.

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31
Q

What do confidence intervals give us?

A

The range in which we can be 95% certain our true value lies, allowing us to make rational inferences despite random variation.

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32
Q

How do you calculate confidence intervals?

A

1). Calculate the observed value (IRR, OR, IR).
2). Calculate the error factor.
3). LCL = observed value/error factor
UCL = observed value x error factor

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33
Q

What are the two types of case control study?

A

1) . Conventional - collect data retrospectively
2) . Nested - case control study within a cohort study
- -> take people with/without the disease from the cohort and ask about their exposures, side effects etc.

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34
Q

What are the advantages of nested case controls?

A

1) . More detail about the participants e.g. Side effects
2) . Allows calculation of an IR still as it is within a cohort study so is based on a defined population (case control alone is not).

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35
Q 
What is the calculation for the IRR in a common disease of a case control study if...
Exposed diseased = A
Exposed undiseased = B
Unexposed disease = C
Unexposed undiseased = D
A

C/C+D

= rate of exposed incidence/rate of unexposed incidence.

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36
Q 
What is the calculation for the IRR or OR in a rare disease of a case control study if...
Exposed diseased = A
Exposed undiseased = B
Unexposed disease = C
Unexposed undiseased = D
A

BC

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37
Q

What is the error factor for case control studies?

A

[2x(root of 1/a + 1/b + 1/c + 1/d)]

e

38
Q

When is the OR used in case control studies?

A

In the rare disease assumption.

39
Q

What are the three types of bias in case control studies?

A

1) . Information bias
2) . Selection bias
3) . Confounding

40
Q

What is selection bias?

A

Bias in how controls are selected.
- if controls become a case, must be classed as one.

  • healthy worker effect
41
Q

How can you minimise confounding in case control studies?

A

1) . Match cases to controls by important confounders.

2) . Adjust for it using logistic regression.

42
Q

What are the 2 types of information bias in case control studies and what do they cause?

A

1) . Non differentiated misclassification (recall bias)
- –> inaccurate measurement often when people forget if they were exposed.
- –> causes shrinkage to the null (OR moves towards 0)

2) . Systematic bias
- –> where the cases have different assessor bias, data collection methods etc
- –> those unexposed think they were exposed
- –> movement to or from the null depending on if the diseased or undiseased got it wrong.

3) . Publication bias
- –> when ones that don’t prove something aren’t published

43
Q

What is information bias in a case control study estimated at?

A

~10%

44
Q

What is a prospective or retrospective case control study?

A

Prospective - the study can be designed so that controls are also monitored for any disease arising and side effects etc are checked.

Retrospective - the usual - people are selected and asked about exposure.

45
Q

What is a prospective or retrospective cohort study?

A

Prospective - start with disease free individuals and follow up for a period of time.

Retrospective - recruit past disease free individuals and classify on their exposure status and subsequent disease status.

46
Q

What is an internal or external cohort study, which calculations are used and how does cohort size affect them?

A

Internal

  • follow 2 groups ourselves
  • if either sub cohort is small, e.f. increases
  • IRR is used

External

  • follow 1 group and compare to a reference population
  • e.f. is based on SMR (which is one value rather than 2 in IRR) so isn’t affected by size.
47
Q

What are the differences between prospective and retrospective studies?

A

Prospective = slower, less unknown confounding (can measure outcome and confounders)

48
Q

What are the advantages and disadvantages of external comparison?

A

+ works better in small groups

  • more prone to selection bias if groups aren’t comparable
  • limited data for reference population
49
Q

What are e advantages and disadvantages of cohort studies?

A

+ good for conditions that change with age
+ good for rare exposures
+ measures multiple outcomes
+ establishes temporal sequence

  • survivor bias
  • takes a long time
  • large/resource intensive
  • falls to unknown confounding
  • results can be influenced by ethics or politics
  • no good for rare diseases
50
Q

How is SMR calculated in external cohort studies?

A

1) . Obtain the age specific incidence rates for reference population for each time period
2) . Multiply rates by correct cells person years for cohort = expected deaths
3) . Calculate SMR

51
Q

How do you account for age change when calculating the SMR in an external cohort study?

A

By plotting a lexis diagram.

52
Q

What are the 3 points a RCT must be?

A

1) . Fair - free from bias or confounding
2) . Controlled - comparison of interventions
3) . Reproducible

53
Q

What are the advantages and disadvantages?

A

+ random allocation = little confounding or bias

  • goes against collective ethics (all patients should have safe, efficient treatment)
  • goes against individual ethics (principles of justice, non malice, benefice and autonomy)
54
Q

Briefly, how is a RCT conducted?

A

1) . Define factors - disease, outcome, treatment
2) . Identify, invite and gain consent from participants
3) . Randomly allocate treatment
4) . Follow up - maximise compliance and minimise drop out
5) . Observe outcomes

55
Q

What are the types of outcome and examples of these?

A

1) . Clinical - death
2) . Pathophysiological - tumour size
3) . Patient centres - quality of life

56
Q

What a primary and secondary outcomes?

A

Primary = the one being measured in sample size calculation

Secondary = any other interests e.g. side effects.

57
Q

What are the features of an ideal outcome?

A 
Cheap
Timely
Reliable
Robust
Appropriate
Simple
Valid
Specific for accurate detection of differences
58
Q

What can differences in treatment in an RCT be due to?

A

1) . Chance
2) . Patient, clinician or assessor bias
3) . One is better than the other

59
Q

What is blinding and what does it avoid?

A

Single, double or triple.
The patient/clinician/assessor does not know what treatment has been assigned to who.

This avoids the placebo effect.

60
Q

What are the features of a placebo and under what conditions can it be used?

A

They are inert and identical in EVERY WAY to the real drug.
The patient must consent to knowing they may not receive a real drug, and a placebo can only be used when no standard treatment available.

61
Q

What is an RCT?

A

A planned experiment that tries to elucidate the most appropriate method of treatment for future patients for a specific disease.

62
Q

What are the two types of trial analysis in RCTs?

A

1) . Pragmatic trial - intention to treat

2) . Explanatory trial - as treated

63
Q

What is a pragmatic trial?

A

Intention to treat
Includes everybody who began the trial = preserves randomisation.
Gives a better indication of how effective the treatment would work in a clinical setting.

64
Q

What is an explAnAtory trial?

A

As treated analysis
Includes only those who have complied with the treatment and stayed in the trial.
Gives a better indication of the physiological effect of the drug
Loses effect of randomisation

65
Q

Why do some not comply in an RCT and how do we maximise compliance?

A

May not comply if:
They don’t understand
They don’t like treatment
They feel no benefit/prefer another treatment

Maximise compliance by:
Making it simple
Asking about side effects and compliance
Monitoring compliance

66
Q

How do we minimise losses to follow up?

A

1) . No coercion into being a participant
2) . Be honest about commitment etc
3) . Maintain contact
4) . Make follow up simple

67
Q

What are the 5 ethical points to be considered in an RCT?

A

1) . Clinical equipoise
- there must be reasonable uncertainty/genuine ignorance as to which treatment is best

2) . Scientifically robust
- safety must be monitored and the trial be of appropriate study design and question.

3) . Ethical recruitment
- those included in the trial must not be at high risk of harm and must benefit from the trial in future.

4) . Valid consent
- must be authorised by a knowledgeable informant
- consent must be given and a cooling off period allowed.

5) . Voluntariness
- no coercion or manipulation into involvement

68
Q

What are the Bradford hill criteria linked to the association?

A

1). Strength of association-
Stronger the association, the more likely its a cause.

2). Specificity of association -
If the outcome is associated with only one specific factor, the more likely its a cause.

3). Consistency of association-
If the association occurs in multiple similar studies, the more likely its a cause.

69
Q

Why may there be inconsistency between association of outcome and exposure in similar studies?

A

The exposure is not a cause
Study design is poor
Outcome may have multiple causes

70
Q

What are the Bradford hill criteria about the link between exposure and outcome?

A

1). Temporal sequence -
If the exposure always precedes the outcome, the more likely its a cause.

2). Reversibility -
If removing the exposure reduces the risk of acquiring the outcome, the more likely its a cause.

3). Dose response -
If an increase in exposure increases risk of acquiring the disease, the more likely its a cause.

71
Q

What are the Bradford hill criteria referring to other evidence?

A

1). Coherence of theory -
If the observed association conforms with current knowledge, the more likely its a cause.

2). Analogy -
If the disease is like others, the more likely its a cause.

3). Biological plausibility -
If a biological mechanism is demonstrated, the more likely its a cause.

72
Q

How can coherence of theory and biological plausibility be limited?

A

Biological plausibility may be limited by current knowledge.

Coherence of theory may lead to inappropriate rejection of unfavourable association = publication bias.

73
Q

What are the explanations for association?

A

1) . Confounding
2) . Selection bias
- -> people selected are unrepresentative of the population
3) . Information bias
4) . Alternate associations
- -> confounding
- -> reverse causality
- -> common cause between the associated things
5) . Chance

74
Q

What are the henle-kochs postulates?

A

1) . Agent is necessary - present in all cases of the disease
2) . Agent is specific - present in cases of that disease only
3) . Agent is sufficient - alone can cause the disease

75
Q

What is the purpose of meta-analysis?

A

Systematically collate study results
Quantify effect sizes and their uncertainty as a pooled estimate
Facilitate synthesis of a large number of study results
Aid interpretation of results with variation in sampling.

76
Q

What do meta-analyses specify?

A

How set of studies is collected
Common categories/variables the study defined
Standardised data extraction used
How sources of variation were allowed for

77
Q

How do you interpret a meta-analysis?

A

Dotted line = pooled OR
Diamond = pooled CL
Line = null value
Size of study’s square = size of error factor

78
Q

What would you talk about when nterpreting meta-analysis results?

A

1) . Overall trend
2) . How many studies are statistically significant
3) . Conclusion from the pooled estimate

79
Q

What are the 3 problems with meta-analyses?

A

1) . Heterogeneity - no 2 studies are ever the exact same.
2) . Publication bias - not involving unfavourable studies in the results
3) . Variation in study quality

80
Q

What could variable quality of study design be due to and how can we solve this?

A

Poor study design or poor protocol implementation (= bias).
Solve by having a set standard which the studies must meet before being involved in the meta-analyses, or scoring each study on its quality, and incorporating this into the study’s weighting.

81
Q

How can you identify publication bias?

A

Funnel plot - size of study plotted against the result. If there’s a lack of studies on the bottom left hand side, publication bias has probably occurred.

Check to see if unpublished trials have been included in the analysis.

82
Q

How can heterogeneity variation be modelled for?

A

A fixed effect model - assumes all studies are estimating th same true value and variation is variation within the study, not between studies.

A random effects model - assumes all studies have their own true value that lies in a range (the distribution of true effect). Variation is between studies also.

83
Q

Compare the fixed effect model and random effects model.

A

Fixed effect =
smaller CL
less equal weighting (more given to smaller studies)
similar point estimate to random effects model

Random effects =
wider CL
more equal weighting (less given to smaller studies)

84
Q

Why is the test for heterogeneity weak?

A

Heterogeneity is hard to detect - only works at a 10% significance level.

85
Q

When will a meta-analysis not be performed on a systematic review?

A

When the studies are heterogeneous = non comparable

86
Q

What is a systematic review?

A

An overview of primary studies that used similar methods to study the same topic.

87
Q

What is a meta-analysis?

A

Quantitative synthesis of results of multiple primary studies on the same topic.

88
Q

What is reporter bias?

A

When if a patient is receiving a placebo, their symptoms etc may be ignored by an assessor who knows they receive the placebo.

89
Q

What is clinical equipoise?

A

The genuine uncertainty over which treatment is better in an RCT.

90
Q

What is ethical recruitment?

A

Recruitment from the region in which the drug will be used

No unethical exclusion from the trial

91
Q

What makes a clinical trial ethical?

A

Clinical equipoise
Ethical recruitment
Scientifically robust
Voluntary consent

92
Q

What is variation?

A

The difference between the actual values and observed values.

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