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1

What is selection bias?

Systematic differences in comparison groups, arising from the selection of participants.

2

What type of bias this this?

 

Systematic differences in comparison groups, arising from the selection of participants.

Selection Bias

3

What is considered a more severe form of selection bias?

Ascertainment Bias

4

What is another name for ascertainment bias?

Information bias

5

What type of bias is this?

 

Subjects belonging to a particular social group have medical records but others have to depend on recall.

Ascertainment / information bias

6

What is length bias?

A systematic error due to the inappropriate selection of long-duration cases.

 

Prevalence is dominated by those who survive for a longer duration. And these patients are qualitatively different from those who die early. Thus the sample may include disproportionately more of those who are healthier and survive longer. The conclusions can not be generalised to those who have less survival time.

7

What type of bias occurs when you are only measuring cases who survive longer, and you miss out on measuring cases who don't survive as long (and therefore might posess different characteristics)?

Length bias

8

Which type of non-RCT measures the exposure first?

Cohort Study

9

What type of study measures the outcome first?

case-control study

10

Which type of study is not conducive to calculating incidence, prevelance, risk & risk ratio, and why?

Case Control Study

Because the incidence is set by the authors

11

What is Berkson Bias?

A specific form of selection bias when a case control study is performed in a hospital. Bias occurs if the exposure increases one’s chance of admission.

12

What type of bias occurs if you are performing a case control study in a hospital, and the exposure which you are measuring increases the chance of admission?

Berkson Bias

13

What type of bias can be reduce by blinding the assessors?

Detection bias / observer bias

14

What sort of bias can be reduced by blinding those who select participants?

Selection bias

15

What is observer bias?

Occurs when the observer unwittingly (or even intentionally) exercises more care about one type of responses or measurements such as those supporting a particular hypothesis than those opposing this hypothesis.

16

What type of bias occurs when the observer exercises more care about one type of responses or measurements such as those supporting a particular hypothesis than those opposing this hypothesis?

Observer Bias

17

What type of bias is recall bias?

Systematic error due to differences in the accuracy or completeness of recall to memory of past events or experiences.

18

What type of bias is a systematic error due to differences in the accuracy or completeness of recall to memory of past events or experiences?

Recall bias

19

What type of bias is  the systematic error due to differences in characteristics between those who choose to participate in a study and those who do not.

Response Bias

20

What is response bias?

Systematic error due to differences in characteristics between those who choose to participate in a study and those who do not.

21

What type of bias describes the situation when a new or experimental test merely identifies the disease earlier than the previous and thus gives the impression that survival is prolonged?

Lead time bias

22

What sort of bias does "Intention To Treat' reduce?

Attrition Bias

23

What is attrition bias?

Systematic differences between groups in withdrawals from a study. Withdrawals from the study lead to incomplete outcome data.

24

How can you reduce attrition bias?

Intention to treat

25

Describe what ITT analysis is

Analysing participants in the groups to which they were randomised, regardless of their compliance.

26

 Describe what per protocol analysis is

Analysing only those participants who were compliant with the treatment / placebo in the group to which they were assigned

27

What is discrete data and give an example?

A type of ordinal data

Whole numbers

eg. number of children (1,2,3,4,>4)

28

What is numerical data?

Data consisting of numberical scores

Includes variable and discrete data

29

What is variable data?

A type of numerical data

Numbers which involve fractions and can be ranked

Eg. length (1cm, 1.25cm, 1.78cm)

30

What is categorical data?

Non-numerical data