1. What is Prevalence Ratio?

The Prevalence Ratio (PR) is a measure of association that compares the prevalence of a condition in an exposed group to the prevalence in an unexposed group. It's commonly used in cross-sectional studies to assess potential risk factors.

2. How Does the Calculator Work?

The calculator uses the Prevalence Ratio formula:

Where:

• \( Prevalence\ exposed \) — Proportion of cases in the exposed group (0 to 1)
• \( Prevalence\ unexposed \) — Proportion of cases in the unexposed group (0 to 1)

Interpretation:

• PR = 1: No association between exposure and outcome
• PR > 1: Positive association (higher prevalence in exposed)
• PR < 1: Negative association (lower prevalence in exposed)

3. Importance of Prevalence Ratio

Details: The prevalence ratio is particularly useful in public health for assessing the strength of association in cross-sectional studies. It's more intuitive than odds ratios when prevalence is high.

4. Using the Calculator

Tips: Enter prevalence values as decimals between 0 and 1. The unexposed prevalence must be greater than 0. For percentages, divide by 100 (e.g., 25% = 0.25).

5. Frequently Asked Questions (FAQ)

Q1: When should I use prevalence ratio vs odds ratio?
A: Use prevalence ratio for cross-sectional studies when outcome is common (>10%). Odds ratio is better for rare outcomes or case-control studies.

Q2: How do I interpret a PR of 1.5?
A: A PR of 1.5 means the prevalence in the exposed group is 1.5 times higher than in the unexposed group.

Q3: What's the difference between PR and risk ratio?
A: PR compares existing cases at one time point (prevalence), while risk ratio compares new cases over time (incidence).

Q4: Can PR be greater than 1?
A: Yes, PR > 1 indicates higher prevalence in the exposed group compared to unexposed.

Q5: How precise should my prevalence values be?
A: For accurate results, use at least 3-4 decimal places, especially when prevalence is low.