Intro to study design

Question 1

What is an exposure give examples?

Answer 1

A causative factor e.g. physiological (height), lifestyle characteristic (exercise) etc.

Question 2

What is an exposure also known as?

Answer 2

Explanatory variable, independent variable, X variable, risk factor, treatment group

Question 3

What is an outcome?

Answer 3

A disease state e.g. periodontal disease

Question 4

What is an outcome also known as?

Answer 4

Response variable, dependent variable, y variable, case/control group, disease group

Question 5

What is a null hypothesis?

Answer 5

No association between exposure and outcome

Question 6

Hypothesis: drinking fruit juice is not associated with dental erosion. In this hypothesis what is fruit juice?

Answer 6

The exposure

Question 7

What are the two common types of studies?

Answer 7

Interventional and Observational

Question 8

What are the two interventional studies?

Answer 8

Experiment and randomised controlled trial

Question 9

What are the 5 types of observational studies?

Answer 9

Cohort, case-control, cross-sectional, ecological, descriptive

Question 10

What is an interventional study?

Answer 10

Investigators test if changing something alters the outcome of the study

Question 11

What is an observational study?

Answer 11

The investigator collects data associated with the occurrence/progression of an outcome with no intervention/manipulation of any kind

Question 12

How is a randomised controlled trial designed?

Answer 12

Subjects randomly allocated to either treatment or control groups, all followed up then outcomes measured and compared

Question 13

What are the two types of cohort study?

Answer 13

Perspective and historical

Question 14

How is a perspective cohort study designed?

Answer 14

Exposure data is collected, then subjects followed up to see if exposed/unexposed develop outcome at different rate (only included if don’t present the outcome of interest)

Question 15

How is a historical cohort study designed?

Answer 15

Exposure data is obtained from historical records then subjects followed to see if have experienced the outcome of interest at any time up until the resent

Question 16

How is a case control study designed?

Answer 16

Cases (with outcome) identified first then controls (without outcome), then frequency of exposure measured retrospectively and compared

Question 17

How is a case control study designed?

Answer 17

Cases (with outcome) identified first then controls (without outcome), then frequency of exposure measured retrospectively and compared

Question 18

How is a cross-sectional study designed?

Answer 18

Exposure and/or outcome data collected at a particular point in time

Question 19

How is an ecological study designed?

Answer 19

Units of analysis are populations or groups of people rather than individuals (e.g. to environmental exposures)

Question 20

How is a descriptive study designed?

Answer 20

Exposure or outcome datant described in terms of time, place, or person

Question 21

Which study design collects data on groups of people rather than individual?

Answer 21

Ecological

Question 22

In which order do the different studies go on the heirachy of evidence?

Answer 22

1. Systemic review & Meta Analysis
2. Randomised controlled trial (eliminate confounding and bias is minimised)
3. Cohort study (temporal sequence clear)
4. Case-control study (attempt to asscertain exposure status before the onset of outcome)
5. Cross-sectional study (measure exposure and outcome at same time)
6. Ecological study (confounding cannot be excluded or accounted for as for population)
7. Descriptive study (no comparison group = patterns difficult to interpret)

Question 23

Before a relationship can be said to be causal what must be ruled out/considered?

Answer 23

Chance

Bias

Confounding

Reverse causality

Question 24

What is chance?

Answer 24

variation that is due to random fluctations i.e. some untreated patients will get better, some treatment groups will still have the disease

Determined if chance by using p-values and confidence limits = assess evidence against the null hypothesis

Question 25

What is Bias?

Answer 25

systematic departure from the true value = misleading results

Question 26

What are the different types of bias (4)?

Answer 26

• Measurement (recall, interviewer, detection)
• Selection (of subjects)
• Loss to follow up
• Performance

Question 27

What is confoudning?

Answer 27

association with third variable that provides an alternative explanation for observed association between exposure and outcome (may or may not have been measured = related to both exposure and outcome)

Question 28

Which type of study is least likely to be affected by confoundng?

Answer 28

Randomised controlled trial (exposure allocated randomly so not associated with any other factors)

Question 29

What is reverse causality?

Answer 29

Alternative explanation for observed association between exposure and outcome whereby outcome causes exposure rather than vice versa (e.g. oral cancer causes body weight)

Only an issue when data on both variables are collected at the same time so dont know which came first without temporal sequence

Question 30

When can something be labelled causal?

Answer 30

• With consistency of evidence across studies in diff populations
• When there is a biologically plusible mechanism that links the two

Question 31

Why is heirachy of evidence only a guide?

Answer 31

Quality also depends on how well the study has been designed (e.g. well designed case control may provide more valid evidence than a poorly designed cohort study)

Question 32

What is a genetic study?

Answer 32

• Migrant, twin and adoption studies
• Sequence of human genome fully mapped (candidate genes/polymorphisms frequently identified & traditional epidemiological studies used to measure associations between genes and outcomes, assess gene-environment interactions and facilitate mendelian randomisation approach)

Question 33

What is the medelian randomisation approach?

Answer 33

Observational -> esp. in cohort studies (need large no. of people)

= instrumental variable approach

Estimate of association between candidate gene (related to modifieable exposure) and outcome unconfounded and not affected by reverse causaulty

• genotypes randomly assigned from parent to offspring (no confoudners)
• Outcomes cant alter genotype (no reverse causality)

Question 34

Which non-genetic approach to investigating assocations between modifiable exposures and outcomes has similarities to mendelian randomisation?

Answer 34

Randomised controlled trial

Question 35

What are the similatrities beterrn mendellian randomisation and randomised control trials?

Answer 35

Question 36

Write a null hypothesis:

Answer 36

No assocation between exposure and outcome in this population

Question 37

In which type of study is data collected at one point in time?

Answer 37

Cross-sectional

Question 38

What issues may there be with collecting information from subjects by questionarre or interview?

Answer 38

• Recall bias -> difficult to remember exact previous smoking habits
• Measurement bias -> Participants may be embarrassed about the questions so may be reluctant to answer or not answer truthfully

Question 39

How could you deal with the issue of smoking as a confounder if designing a study to assess the association between periodontitis and coronary heart disease?

Answer 39

• Ensure detailed smoking data collected (adjusta analyses)
• Restrict study to non-smokers only (may reduce generalisability)

Question 40

What is the main difficulty with using a mendelian randomisation approach in general?

Answer 40

Can only be used when it is possible to identify appropriate genetic variants