Key Concepts in Absolute Risk and Group Comparisons

Vocabulary flashcards covering Absolute Risk concepts, CER/EER, ARR, NNT, RR, and RRR with their definitions and relationships.

Absolute Risk (AR)

Baseline probability of an event in a specific group; basically, how likely the bad outcome is in that group.

Control Event Rate (CER)

Absolute risk of the event in the control group; baseline risk (example: 50% if 50/100).

Experimental Event Rate (EER)

Absolute risk of the event in the treatment/experimental group; risk after the intervention.

Absolute Risk Reduction (ARR)

Difference between CER and EER; ARR = CER − EER (e.g., CER 0.50, EER 0.30 → ARR 0.20 or 20%).

Number Needed to Treat (NNT)

Number of patients who must be treated to prevent one additional bad outcome; NNT = 1/ARR (e.g., ARR = 0.20 → NNT = 5).

Relative Risk (RR)

Ratio of risk in the treatment group to the control group; RR = EER / CER (e.g., EER 0.30, CER 0.50 → RR = 0.60).

Relative Risk Reduction (RRR)

Proportion by which risk is reduced in the treatment group relative to control; RRR = 1 − RR (e.g., RR = 0.60 → RRR = 0.40 or 40%).