In a study, a prevalence ratio of 0.6 for a disease comparing Group A to Group B implies which group has the higher disease prevalence?

In a study, a prevalence ratio of 0.6 for a disease comparing Group A to Group B implies which group has the higher disease prevalence?

• A. Group B (denominator)
• B. Group A (numerator)
• C. Both exposures have equal prevalence
• D. Cannot determine from the ratio alone

Answer: (A)

The key idea is that a prevalence ratio compares the prevalence in two groups by dividing the prevalence in the first group (numerator) by the prevalence in the second group (denominator). A value of 0.6 means Group A’s prevalence is 0.6 times Group B’s. Put differently, P_A = 0.6 × P_B, so Group B has the higher disease prevalence. If the ratio were above 1, Group A would have the higher prevalence; if it were 1, both groups would have equal prevalence.

The key idea is that a prevalence ratio compares the prevalence in two groups by dividing the prevalence in the first group (numerator) by the prevalence in the second group (denominator). A value of 0.6 means Group A’s prevalence is 0.6 times Group B’s. Put differently, P_A = 0.6 × P_B, so Group B has the higher disease prevalence. If the ratio were above 1, Group A would have the higher prevalence; if it were 1, both groups would have equal prevalence.