3. Cause and error

Question 1

What are the effects of random error?

Answer 1

Sampling variability
Dependent and / or independent variables are misclassified
…Reduced likelihood of detecting a significant effect

Question 2

Two types of selection bias?

Answer 2

1. Selection of cases or controls on the basis of an exposure which is associated with the disease in question
2. Non-random allocation of patients to treatment groups in a clinical trial

Question 3

What is information/recall bias?

Answer 3

people with a disease recall their history differently to people that don’t have the disease

Question 4

What is internal validity?

Answer 4

The testing of an association by cross checking within a study - e.g. can ask the same question in two different ways.

Question 5

When do confounders occur?

Answer 5

Confounders occur when more than one variable is associated with an outcome and the two variables are associated

Question 6

What is a false association?

Answer 6

When a significant association between an exposure and disease is found but there is not a true difference in the population

Question 7

What is a type 1 / beta error?

Answer 7

Occurs when a difference is detected between two samples which are actually from the same population