1. Research Design

Question 1

When is an experimental study used?

Answer 1

To investigate interventions e.g., compare patient response after a treatment vs control

Question 2

When is an observational study used?

Answer 2

When no intervention takes place. This is used to enable inferences about diseases through natural observation of groups defined by their exposure or disease status

Question 3

What is a dependent variable?

Answer 3

What we measure. The “outcome” or “criterion” variable.

Question 4

What is an independent variable?

Answer 4

What we manipulate or vary systematically. The “predictor” variable.

Question 5

What are the pros and cons of between-subjects designs?

Answer 5

Advantages: comparison of different groups (e.g., gender, age, ethnicity), eliminates risk of practice or order effects.

Disadvantages: unidentified differences in groups may affect results, not always clear if difference is due to IV or a confounding variable.

Question 6

What are the pros and cons of within-subjects designs?

Answer 6

Advantages: useful to monitor the effects on same individuals, controls for individual differences.

Disadvantages: Order/practice effects can confound results (reduced with counterbalancing).

Question 7

What is a control condition?

Answer 7

It is identical to other conditions, except the proposed causal factor (IV) is not present. Acts as a baseline for comparison with the causal condition.

Question 8

What are single and double blind trials?

Answer 8

Single blind: either the investigator, patient, or assessor is blind to the allocation.

Double blind: participant and researcher do not know which treatment the ppt is taking.

Aim is to reduce selection and observer bias.

Question 9

What is an explanatory RCT?

Answer 9

Tests efficacy with carefully selected participants in highly standardised conditions

Question 10

What is a pragmatic RCT?

Answer 10

Tests effectiveness in real life practice under more flexible conditions

Question 11

What are possible sources of bias with RCTs?

Answer 11

Blinding: clinicians/ researchers are often unavoidably aware of treatment allocation, which could cause bias

Drop out: non-random drop out could bias results

Treatment adherence: participants may stop, miss sessions or receive additional treatment

Question 12

What are the pros and cons of RCTs?

Answer 12

Advantages: avoids confounding variables as comparison groups should only differ in intervention/exposure status, causal hypothesis can be tested, effect of intervention can be measured.

Disadvantages: costly and difficulty, ethical issues, efficacy vs effectiveness issues

Question 13

What are the pros and cons of experimental studies?

Answer 13

Advantages: repeatability due to controlled conditions, controllability.

Disadvantages: artificial, representativeness of participants, limited number of variables can be manipulated, control of relevant influencing variables.

Question 14

What are the three types of observational studies?

Answer 14

Cross-sectional, case-control and cohort.

Question 15

What is a cross-sectional study used for?

Answer 15

Used to estimate prevalence (point, period, lifetime). And used to measure association.

Question 16

What are the pros and cons of cross-sectional studies?

Answer 16

Advantages: good at estimating prevalence, maximise completeness of data, useful for describing distribution of continuous variables in a population.

Disadvantages: cannot establish causality, cannot establish incidence (new cases), generalisability is limited by size and representativeness of sample.

Question 17

What is a case-control study used for?

Answer 17

To help determine if an exposure is associated with an outcome. Compares prior expose and frequency. Cases and controls can be matched on an individual or group basis on characteristics that need to be controlled for (e.g., age, sex).

Question 18

What are the pros and cons of case-control studies?

Answer 18

Advantages: useful for rare outcomes and outcomes with long latency, can examine multiple exposures, current hypotheses can be tested.

Disadvantages: prone to selection bias and information bias, temporal relationship between exposure and outcome may be difficult to determine, not suitable for studying rare exposures, cannot establish incidence.

Question 19

What is a cohort study?

Answer 19

This is to observe a cohort over time. They are usually a better option than case-control studies as the exposure is measured before the outcome, avoiding recall bias and “reverse causality”.

Question 20

What are the types of cohort studies?

Answer 20

Prospective: cohort is formed and followed over time, temporal relationship between exposure and outcome can be recognised.

Retrospective: data gathered for a cohort formed in the past, outcome is determined by exposure status.

Population: large cohort is recruited and followed e.g., birth cohort, allows a large number of common exposures to be considered in relation to multiple outcomes (test multiple hypotheses).

Question 21

What are the pros and cons of cohort studies?

Answer 21

Advantages: can establish incidence, suitable for rare exposures, multiple outcomes can be examined, participants in a cohort can be matched.

Disadvantages: can be expensive and take many years, attrition bias, not ideal for outcomes with long latency (unless using retrospective design), unsuitable for rare outcomes, new knowledge can develop which is not accounted for in the design.

Question 22

Why is measuring mental health challenging?

Answer 22

Study and outcome are only as strong as the measures used. Measurement is difficult in MH as is influenced by subjective experience, there is considerable variability in clinician’s diagnoses, little/no biological markers, reliance on questionnaire-based assessments.

Question 23

What is reliability?

Answer 23

The consistency of a measure when applied repeatedly under similar circumstances.

Question 24

What is validity?

Answer 24

An expression of the degree to which a measurement measures what it purports to measure.

Question 25

How can reliability be assessed?

Answer 25

Test-retest, calculating inter-rater or inter-observer reliability (or inter-interviewer); operationaling behaviours, Cronbach’s alpha, split-half method (for questionnaires).

Question 26

Explain stratified sampling

Answer 26

1. Identify the different types of people that make up the target population
2. Calculate the proportions required to ensure the sample is representative
3. Create a variable list where any factors that could impact outcome are listed
4. The relative percentage of each group in the sample is calculated as per the target proportion

Sample is highly representative and therefore generalisable to target population

Question 27

Explain opportunity sampling

Answer 27

Selects ppts from target population as they are available and willing to take part (convenience sampling).

Advantages: straight forward and quick

Disadvantages: less likely to be representative

Question 28

Explain systematic sampling

Answer 28

1. Calculate total number in target population
2. Decide sample size
3. Select every ‘N’th number

Provides a representative sample but requires a large target sample

Question 29

What are the four types of randomisation?

Answer 29

Simple, block, stratified, covariate adaptive

Question 30

Explain simple randomisation

Answer 30

Roll of a dice, toss of a coin etc.

Valid for trials where there are more than 200 participants, but problematic for less than 100 due to risk of sampling error

Question 31

Explain block randomisation

Answer 31

divide participants into subgroups (blocks), ensuring that the variability of characteristics is similar, so that the groups do not differ systematically.

Question 32

Explain stratified randomisation

Answer 32

Similar to stratified sampling. Ppts are allocated to blocks, and blocks are randomly allocated to treatment/control group.

Question 33

Explain covariate adaptive randomisation

Answer 33

Allows continuous allocation to groups, by keeping track of prior participants and their characteristics. Probability of being allocated to a group changes depending on the current participants. Participants are assigned by calculating the least imbalance across groups in terms of covariates by using an algorithm.