Session 2 - Ratios, Risk + Studies

Question 1

What is the difference between probability and statistics?

Answer 1

Probability is the chance that something will happen. Statistics is inferring about the population from a sample. E.g. Probability is given the information in the box, what is in your hand when you pick something out, and statistics is using the information in your hand to tell you what’s in the box.

Question 2

What qualities must a sample population have?

Answer 2

Unbiased

Representative

Question 3

What are the 2 types of error in a study?

Answer 3

Chance (random error) - due to sampling variation.

Bias (systematic error) - the difference between the true and expected value.

Question 4

As you increase the sample size, do chance and bias increase or decrease?

Answer 4

Chance decreases, bias stays the same.

Question 5

Name and describe the 2 types of bias.

Answer 5

Selection bias - study sample is not representative of entire population e.g. Doing obesity study outside McD’s.
Information bias.

Question 6

Name the 4 types of information bias.

Answer 6

• recall - differences in recollection from participants
• observer/interviewer - person may have preconceived expectations that influence result
• measurement - differences in measurement of participants
• misclassification - participants put into wrong group

Question 7

What is the definition of prevalence?

Answer 7

The number of people who have a disease at a given point in time (old and new cases).

Question 8

What is the definition of incidence?

Answer 8

The number of new cases of a disease within a given time frame (new cases only). Measure as the number of new cases/sum of patient time at risk.