S1 Hadpop

Question 1

When looking at relationships between two variables, what do you need to consider?

Answer 1

Chance, bias, confounding factors

Question 2

Define bias

Answer 2

Preference to a particular perspective

Question 3

Define confounding factor

Answer 3

Factor that affects both exposure and outcome but is not in the causal pathway

Question 4

What is deterministic causality

Answer 4

Validation of a hypothesis by systematic observations to predict with certainty future events

Question 5

Define stochastic causality

Answer 5

Assessment of a hypothesis via systematic observations to give the likelihood of future events

Question 6

What is the census?

Answer 6

Simultaneous recording of demographic data by the government at a particular time to all people who live in a particular territory

Question 7

Features of Census

Answer 7

Run by government 
Covers defined area
Personal enumeration
Simultaneous throughout defined area
Universal coverage
Regular intervals

Question 8

Three population characteristics the census looks at

Answer 8

Population size
Population characteristics
Population structure
SCS

Question 9

Crude birth rate

Answer 9

Number of live births per 1,000 population

Question 10

General fertility rate

Answer 10

Number of live births per 1,000 females aged 15-44

Question 11

Total period fertility rate

Answer 11

Average number of children that would be born to a hypothetical woman in her life

Question 12

Fecundity

Answer 12

Physical ability to reproduce

E.g. More sterilisation and hysterectomies reduces fecundity

Question 13

Fertility

Answer 13

Realisation of the potential of births

Question 14

Crude death rate

Answer 14

Number of deaths per 1,000 of the population

Question 15

Age specific death rate

Answer 15

Number of deaths per 1,000 in an age group

Question 16

Standardised mortality rate (SMR)

Answer 16

Compares observed number of deaths with number of expected if the age sex distributions of the populations were identical so it adjusts for age sex confounding

Question 17

Define incidence

Answer 17

Number of cases that have occurred over a period of time

New events/ person x time (years)

Question 18

Define prevelance

Answer 18

Number of people affected by the disease

Number of cases/ number of people

P = I x L

Question 19

P<=0.05 means results are

Answer 19

Statistically significant
Enough evidence to reject the hypothesis
This is when the null hypothesis value is outside the 95% confidence interval

Question 20

Cohort study features

Answer 20

Recruit outcome free individuals
Exposed and unexposed groups
Looks forward in time
Calculate IRR (incidence rate ratios) to give relative risk (exposed/unexposed)

Question 21

Cohort study internal v external comparison

Answer 21

Internal comparison

• divide cohort into degrees of exposure
• calculate IRR and e.f.
• more random variation as it is smaller group

External comparison

• compare to external reference pop
• calculate SMR as often no incidence data

Question 22

Healthy worker effect

Answer 22

If people are in work they are more likely to be healthy compared to the rest of the population so likely to get SMR under 100

Question 23

Case control study

Answer 23

• Get a group of cases
• Classify into whether they are have exposed or not
• Work out odds ratio (AD/BC) - precision affected by number of controls

Question 24

Types of bias can include

Answer 24

Selection
Information
Recall

Question 25

Cohort study v Case control study

Answer 25

Cohort more time consuming and expensive Cohort better for rare exposures Case control better for rare outcomes Case control prone to selection and information bias (population of sampling not defined so cannot work out IR etc)

Question 26

Cause and effect relationship - Henle-Koch's postulates

Answer 26

- Agent must be present in every case of the disease - Agent must not be found in cases of any other disease - Agent must be capable of reproducing disease in experimental animals and must be recovered from experimental disease produced

Question 27

Bradford Hill Criteria for Causality

Answer 27

``` SCS DRT CBA Strength of association Consistency of association Specificity of association Dose response Reversibility Temporal sequence Coherence of theory Biological plausibility Analogy ```

Question 28

Steps involved in randomised controlled trials (RCTs)

Answer 28

- Define disease, treatments, possible bias and confounders etc - Identify source of eligible patients, recruit and consent them - Allocate participants to treatments fairly, random allocation minimises allocation bias and confounding - Follow up patients in identical ways - Compare outcomes fairly - Minimise losses to follow up and non compliance with treatment

Question 29

What is the placebo effect?

Answer 29

Placebo is inert substance that appears identical to the active formulation. Placebo effect is the psychological benefit derived from being on the drug or the intervention. Placebo should only be used if no standard treatment is available

Question 30

Explanatory (as treated) v Pragmatic (intention to treat) analysis

Answer 30

Explanatory (as treated) - those who completed follow up and complied with treatments analysed - loses randomisation as non compilers systematically different to compliers Pragmatic trial (intention to treat) - Analyses according to original allocation to treatment groups - Looks at likely effects of using treatments in routine clinical practice and preserves effects of randomisation (minimises selection bias and confounding)

Question 31

Issues to consider in a clinical trial (RCT):

Answer 31

``` SCEVV Scientifically robust Clinical equipoise Ethical recruitment Valid consent Voluntariness ```

Question 32

What is a systematic review?

Answer 32

Overview of primary studies that use explicit and reproducible methods May do meta analysis (quantitative synthesis of results of two or more primary studies that addressed hypothesis in same way)

Question 33

What is a meta analaysis

Answer 33

Quantitative synthesis of the results of two or more primary studies that addressed same hypothesis in the same way. In meta analysis the odds ratio and 95% CIs are calculated for all the studies and then combined to give pooled estimate odds ratio. Can create forest plot.

Question 34

Fixed effect model v random effects model for pooled estimate odds ratio in forest plot

Answer 34

Fixed effect model assumes studies estimating same effect size Random effects model assumes studies are estimating similar effect size, not the same. Wider 95% confidence interval, more equal weighting of studies

Question 35

What is publication bias?

Answer 35

Studies that have statistically significant or favourable results are more likely to be published than those with non statistically significant or unfavourable results esp small studies. Can use funnel plot to look ar whether there is a balance of studies.