Lecture 6

Question 1

When being able to make a casual inference we need to establish…

Answer 1

… that the exposure occurred before the outcome

Question 2

Our aim in a research study is to obtain…

Answer 2

… a reliable estimate of the impact of the intervention or exposure on the outcome of interest

Question 3

What we need in a hypothesis to make it specific enough to test

Answer 3

• defined population
• a ‘quantity’
• time frame

Question 4

How to calculate RR

Answer 4

• proportion

Question 5

What does RR show

Answer 5

A summary of the relationship between risk of cardiovascular disease when taking vitamin D supplicants vs the risk when not taking them is know as the relative risk

Question 6

Sources of error in analytic studies

Answer 6

Sources of error in:
- how we set up our study or design

Question 7

What is confounding

Answer 7

• a distortion of the association between exposure and outcome caused by the presence of a third facter
• a confounded is a variable that caused distortion

Question 8

To be a confounder, a variable must be both…

Answer 8

• associated with the exposure (idependent of outcome)
• associated with the outcome (independent of exposure)

May not just be an intermediate link in the ‘casual pathway

Question 9

Confounding pathway in an observational study

Answer 9

• might be systematic differences between study and control group

Question 10

How might you get confounding in an intervention study?

Answer 10

• during random allocation you cancel out confounder and can be confident in results

Question 11

Two types of bias in analytic study

Answer 11

• selection bias
• information bias

Question 12

What is selection bias

Answer 12

• systematic error arising form the way participants are selected for inclusion in the study

Question 13

How does selection bia occur in an analytic study

Answer 13

• if the selection process causes a systematic difference between the groups of participants selected for the study

Question 14

Is the issue of representativeness bias or a generalisability issue

Answer 14

• prospective analytic studies rarely obtain participants through random sampling of population
• the issure of represtantativeness must be considered, but for analytic studies we consider it a generalisability issue rather then bias

(Generalisation doesn’t represent who you’re looking for - need a confident inference)

Question 15

What is information bias?

Answer 15

• systematic error arising form the way study information was obtained, interpreted and recorded

Question 16

In an analytic study when is information bias a particular problem..

Answer 16

• if there are systemic differences in the information obtained from groups under comparison in the study

Question 17

Information bias may be introduced by the:

Answer 17

• observer
• study individual (respondent)
• instruments used to collect the data ( e.g badly designed questionaire)
• missing measurements (e.g from loss to follow-up in a prospective missing)

Question 18

Non response to a measurement is generally considered________ but non response to participation in the study can be considered ______

Answer 18

Information bias
Selection bias

Question 19

If people drop out of an observational analytic study

Answer 19

• wont get a good estimate
• groups will be more similar
• can’t use two different selection groups - there will be selection bias
• if randomly people missing from both groups - there wont be a systematic difference

Question 20

Bias in a RCT

Answer 20

• people may forget to take supplement or accidentally take it influencing the true difference

Question 21

Classification by purpose of study

Answer 21

• descriptive (describe things)
• analytic (testing hypothesis)

Question 22

Classification by form of the design

Answer 22

• experimental (researcher intervenes)
• observational (researcher observes)

Question 23

Analytic, experimental, prospective

Answer 23

• randomised control trial

Question 24

Randomised control trial

Answer 24

• analytic
• experimental
• prospective

Question 25

Cohort study

Answer 25

• analytic
• observational
• usually prospective

Question 26

Analytic, observational, usually prospective

Answer 26

Cohort study

Question 27

Analytic, observational, retrospective

Question 28

Answer 28