Introduction to Bias

Question 1

What is Selection Bias ?

Answer 1

Error in the process of selecting participants for the study (non representative to the real population) or/and assigning them to particular arm of the study (e.g. in RCTs)

Question 2

What is Attrition Bias ?

Answer 2

When those patients who are lost to follow-up differ in a systematic way to those who did return for assessment or clinic.

Question 3

What is Observer Bias ?

Answer 3

When variables are reported differently between assessors

Question 4

What is Procedure Bias ?

Answer 4

Subjects in different arms of the study are treated differently (other than the exposure or intervention)

Question 5

What is Response bias ?

Answer 5

When the research materials (e.g., questionnaires) prompt participants to answer or act in inauthentic ways through leading questions.

Question 6

What is Misclassification Bias ?

Answer 6

Occurs when a variable is classified incorrectly

Question 7

What is Recall Bias ?

Answer 7

Systematic error due to differences in accuracy of recall to recall of past events / experiences; subjective interpretation

Question 8

How do we reduce Bias ?

Answer 8

1 - Randomisation (experimental analytic studies)
Random sampling methods help ensure that your sample doesn’t systematically differ from the population.

2- Masking
Wherever possible, you should hide the condition assignment from participants and researchers through masking (blinding).
Participants’ behaviours or responses can be influenced by experimenter expectancies and demand characteristics in the environment, so controlling these will help you reduce systematic bias.