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Flashcards in S1 Hadpop Deck (35):
1

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

Chance, bias, confounding factors

2

Define bias

Preference to a particular perspective

3

Define confounding factor

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

4

What is deterministic causality

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

5

Define stochastic causality

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

6

What is the census?

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

7

Features of Census

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

8

Three population characteristics the census looks at

Population size
Population characteristics
Population structure
SCS

9

Crude birth rate

Number of live births per 1,000 population

10

General fertility rate

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

11

Total period fertility rate

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

12

Fecundity

Physical ability to reproduce
E.g. More sterilisation and hysterectomies reduces fecundity

13

Fertility

Realisation of the potential of births

14

Crude death rate

Number of deaths per 1,000 of the population

15

Age specific death rate

Number of deaths per 1,000 in an age group

16

Standardised mortality rate (SMR)

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

17

Define incidence

Number of cases that have occurred over a period of time

New events/ person x time (years)

18

Define prevelance

Number of people affected by the disease

Number of cases/ number of people

P = I x L

19

P<=0.05 means results are

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

20

Cohort study features

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

21

Cohort study internal v external comparison

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

22

Healthy worker effect

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

23

Case control study

- 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

24

Types of bias can include

Selection
Information
Recall

25

Cohort study v Case control study

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)

26

Cause and effect relationship - Henle-Koch's postulates

- 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

27

Bradford Hill Criteria for Causality

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

28

Steps involved in randomised controlled trials (RCTs)

- 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

29

What is the placebo effect?

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

30

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

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)

31

Issues to consider in a clinical trial (RCT):

SCEVV
Scientifically robust
Clinical equipoise
Ethical recruitment
Valid consent
Voluntariness

32

What is a systematic review?

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)

33

What is a meta analaysis

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.

34

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

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

35

What is publication bias?

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.