Measurement of Disease Occurrence and Treatment Effects

Question 1

Prevalence

Answer 1

Proportion of population who has a disease at a point in time. Obtained in cross-sectional studies

diseased population/ total population

Question 2

Incidence

Answer 2

The rate of people developing a disease in a population within a specified time frame

new disease cases/ total population (per unit time)

Question 3

Relative Risk (RR)

Answer 3

The ratio of disease incidence in an exposed population compared to disease occurrence in non-exposed population.

(Exposed diseased/ total exposed) / (non-exposed diseased/ total non-exposed)

RR gives value of >0
RR = 1: no exposure effect
RR < 1: exposure protective
RR > 1: exposure increases outcome

Question 4

Relative risk reduction

Answer 4

Measures the strength of the impact of an exposure or treatment. given as 1 - RR

Question 5

Odds ratio (OR)

Answer 5

Gives the ratio of ODDS of disease in exposed person to disease in non-exposed person

(diseased exposed/ healthy exposed) / (diseased non-exposed/ healthy non-exposed)

Gives value >0
OR = 1: no association between risk factor and disease
OR < 1: risk factor protective
OR > 1: positive correlation between risk factor and disease

Question 6

Risk difference

Answer 6

The difference in risk of an outcome in a control vs treatment group. Either:

Absolute risk increase or absolute risk reduction

Question 7

Absolute risk reduction

Answer 7

The difference in risk of outcome in a control vs treatment group, where the treatment decreases the risk.

outcome% of control group - outcome% of treatment group

Question 8

Absolute risk increase (ARI)

Answer 8

The difference in risk of an outcome in a control vs treatment group, where the treatment increased the risk of an outcome.

outcome% in treatment group - outcome% in control group

Question 9

Number needed to treat (NNT)

Answer 9

The number of people needed to treat in order to prevent 1 undesired outcome.
1/ARR

Question 10

Number needed to harm (NNH)

Answer 10

Number of patients who need to be treated to cause one additional patient harm