Measures of risk
- Risk factors: variables or attributes that increase the probability of developing disease or injury
- The variables in the formula below stand for the following:
|
With disease |
Without disease |
| Exposed |
a |
b |
| Not exposed |
c |
d |
Absolute risk
- ∼ Incidence rate
- Measures the probability of acquiring disease/injury in a given study population
- Used in cohort studies
- Formula: (number of new cases) / (total individuals at risk of developing disease) = (a + c)/(a + b + c + d)
- The risk of an outcome (e.g., disease) among one group compared to the risk among another group (or control group)
- Measures how strongly a risk factor (e.g., death/injury/disease) in exposed individuals is associated with an outcome
- Used in cohort studies
- Considered statistically significant if the corresponding p-value is < 0.05
- Formula: (incidence of disease in exposed group) / (incidence of disease in unexposed group) = (a/(a + b))/(c/(c + d))
- (RR) is the ratio of risk in the experimental group (experimental event rate, EER) to risk in the control group (control event rate, CER)
To recap
- EER = rate at which events occur in the experimental group
- CER = rate at which events occur in the control group
For example, if we look at a trial comparing the use of paracetamol for dysmenorrhoea compared to placebo we may get the following results