Chapter 12 Estimating Risk

Risk

The chance that something, like a disease, will happen. Example: If 3 out of 10 people get sick, A: 3/10 or 30%.

Absolute Risk (AR)

Also called incidence; it tells you how common a disease is in a group. Example: If 20 out of 100 exposed people get sick,

Relative Risk (RR)

It tells you how much more likely the exposed group is to get sick compared to the unexposed group. Formula: Risk in exposed ÷ Risk in unexposed. Example: If exposed group has 20% risk and unexposed has 10%, A = 2.

Excess Risk

The extra risk caused by the exposure. Formula: Risk in exposed - Risk in unexposed. Example: If exposed = 20%, unexposed = 10%, A: 10%.

Odds

A way of saying how likely something is compared to it not happening. Example: If 2 people are sick and 8 are not. 2/8

Odds Ratio (OR)

Compares the odds in the exposed vs. unexposed groups. Example: Odds of disease in smokers vs. nonsmokers.

Attack Rate

A special kind of risk used during outbreaks. Formula: # of new cases ÷ total people at risk. Example: 10 people get food poisoning out of 50 who ate at a buffet

Randomized Controlled Trial (RCT)

A study design where people are randomly assigned to treatment or control groups, best for proving causation.

Cohort Study

A study design that groups people by exposure and follows them over time to see who gets the disease. Useful for studying how an exposure affects risk.

Case-Control Study

A study design that starts with people who have the disease and compares them to those who do not, looking back at exposure.

Association

When two things happen together (like smoking and lung cancer); not the same as causation.

Causation

When one thing actually causes another; requires stronger evidence than association.

Incidence

Another name for absolute risk is blank

Formula for Excess Risk

Risk in exposed - Risk in unexposed.

Formula for Relative Risk

Risk in exposed ÷ Risk in unexposed.

Interpretation of RR = 1

Indicates no difference in risk between exposed and unexposed.

Interpretation of RR > 1

Indicates that the exposure increases risk.

Interpretation of RR < 1

Indicates that the exposure lowers risk.

Limitation of RR in Case-Control studies

Cannot be calculated as you don’t know how many were at risk; starts with diseased individuals.

Calculation of OR

can be calculated in both cohort and case-control studies.

Risk vs. Odds Ratio

RR uses risk, OR uses odds; RR is often easier to understand.

When is OR a good estimate of RR?

When the disease is rare.

Importance of Absolute Risk

It shows how likely someone is to get the disease, helping both doctors and patients.

What does RR measure?

How much the exposure increases or decreases risk.

What does OR measure?

How much more likely the exposure is in cases compared to controls.