2 Epidemiology Study Designs

Question 1

A hypothesis usually takes the form

Answer 1

Exposure X is associated with an increase/decrease risk of outcome Y.

Question 2

2 types of error

Answer 2

systematic error (referring to bias)

random error (referring to imprecision).

Question 3

what is bias

Answer 3

systematic error or derivation from the truth of results

due to incorrect measurements or non-representative sample.

Question 4

Selection bias

Answer 4

allocation of subjects not representative of whole population. Controlled by randomisation with concealment.

Question 5

Performance bias

Answer 5

performing intervention different for different patients, results are not controlled. Controlled by double blinding, use of placebo.

Question 6

Detection bias

Answer 6

Evaluation of outcomes is different between groups. Controlled by blinded outcome assessment that doesn’t pinpoint only one group.

Question 7

Measurement/observation/information bias

Answer 7

systematic error of poor measurement of outcomes. Controlled by review of measurement tools.

Question 8

Recall/responder bias

Answer 8

inaccurate responses/recalled. Controlled by a good study design.

Question 9

Attrition bias

Answer 9

different flow up between groups, + drop outs. Controlled by analysis of subjects as randomised.

Question 10

What is confounding

Answer 10

non-causal association observed due to third variable.

describes an association that is true but potentially misleading.

Question 11

How can confounding be controlled

Answer 11

design phase:
randomising
restricting
matching parts of the population.

analysis stage:
stratification of results
adjusting by statistical modelling.

Question 12

Explain reliability

Answer 12

Reliability tools measure accurately and consistently. = PRECISION

Test-retest reliability: results consistent by measuring twice.

Inter-rater reliability: assesses the degree of agreement between judges.

Question 13

Explain validity

Answer 13

refers to the legitimacy of the research = ACCURACY

Internal validity: correct results for group studied

External validity: generalisable results

Construct validity: test measure what it claims to be measuring

Question 14

Case study

Answer 14

Reports observations of single individual, case series is an aggregate.

Question 15

Ecological study

Answer 15

looks at groups of people rather than individuals.

Compares disease frequencies between different populations at 1 time or 1 population at different times.

Question 16

Cross-sectional study

Answer 16

Also called a prevalence study

measures prevalence and presence/absence of exposure.

only 1 point in time no past/future

Question 17

Case-control study

Answer 17

1 group has disease other does not, look back and determine how many from each group had the risk factor.

Retrospective

Uses O.R

Question 18

Cohort study

Answer 18

Comparison of groups of people who share common characteristics within a define time period

Prospective = see who develops

Retrospective = exposure and outcome already occurred

Uses R.R

Question 19

RCT

Answer 19

Patients randomly allocated to treatment and control group, compare outcomes due to intervention

Randomisation controls for confounding by distributing confounders evenly

Question 20

Cross over trial

Answer 20

normal RCT, washout period, then swap intervention and controls groups.

Question 21

n of 1 trial

Answer 21

cross over trial with only one patient

Question 22

Cluster of RCT

Answer 22

Unit of measure is not an individual but a group. Often used in communities where there is a risk of contamination

Question 23

What is a systematic review

Answer 23

answers a defined research question by summarising evidence of eligibility criteria.

Question 24

What is a meta analysis

Answer 24

statistical methods to summarise results of studies

Question 25

Narrative review

Answer 25

broad
author can use literature to support view point
limited critical appraisal

Question 26

characteristics of systematic review

Answer 26

minimise bias
answers question
summary of data
regularly updated.

Question 27

Steps of a meta analysis

Answer 27

1. Formulate structured clinical question
2. Conduct extensive search documenting search strategy
3. Select studies for inclusion, justify exclusion
4. Assessment of methodological quality of including studies
5. Abstraction of relevant data
6. Data synthesis (meta-analysis)

Question 28

Describe blinding

Answer 28

people are unaware of which trial group the participants are in.

minimise performance and detection bias such as the care that is provided to the comparison groups.