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Epidemiology Calculator

Calculate odds ratio, relative risk, and 2x2 table analysis with confidence intervals

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Odds Ratio Calculator with 95% Confidence Intervals

Calculate odds ratios from 2x2 contingency tables with instant confidence intervals. Perfect for case-control studies and diagnostic test accuracy analysis. Includes chi-square test and Fisher's exact test for statistical significance.

  • Instant odds ratio calculation
  • 95% confidence intervals
  • Chi-square and Fisher's exact tests
  • APA-formatted output

Relative Risk Calculator for Cohort Studies

Compute relative risk and risk ratios for prospective cohort studies. Analyze exposure-disease relationships with comprehensive statistical measures including attributable risk and population attributable fraction.

  • Relative risk calculation
  • Risk difference analysis
  • Attributable risk percent
  • Population attributable fraction

2x2 Contingency Table Analysis

Complete 2x2 table analysis with chi-square test for association, Fisher's exact test for small samples, and comprehensive epidemiological measures. Ideal for cross-sectional and case-control studies.

  • Chi-square test of independence
  • Fisher's exact test
  • Yates' continuity correction
  • Effect size measures

How to Use the Epidemiology Calculator

Step 1: Enter Your Data

Input your 2x2 table data with exposed/unexposed groups and disease/no disease outcomes. Ensure accurate cell counts for reliable results.

Step 2: Select Analysis Type

Choose between odds ratio (case-control), relative risk (cohort), or comprehensive analysis including both measures with confidence intervals.

Step 3: Interpret Results

Review calculated measures, confidence intervals, and p-values. Use our interpretation guide to understand clinical and statistical significance.

When to Use RR vs OR: Epidemiological Study Comparison

Study Design Measure Best Use Case Interpretation
Case-Control Study Odds Ratio (OR) Rare diseases, retrospective analysis OR > 1: Increased odds of exposure
Cohort Study Relative Risk (RR) Common outcomes, prospective follow-up RR > 1: Increased risk in exposed group
Cross-sectional Prevalence Ratio Disease prevalence comparison PR > 1: Higher prevalence in exposed
Clinical Trial Number Needed to Treat Treatment effectiveness Lower NNT: More effective treatment

Frequently Asked Questions

How to calculate odds ratio from 2x2 table?
Enter your 2x2 table data (exposed/unexposed vs disease/no disease). The odds ratio is calculated as (a×d)/(b×c) where a, b, c, d are the four cells of your contingency table. Our calculator provides instant results with 95% confidence intervals and statistical significance testing.
What is the difference between odds ratio and relative risk?
Odds ratio compares odds of disease between exposed and unexposed groups, used in case-control studies. Relative risk compares risk of disease between groups, used in cohort studies. OR approximates RR when disease is rare (<10%). Both measure association strength but have different interpretations.
When should I use Fisher's exact test vs Chi-square?
Use Fisher's exact test when expected cell counts are <5 in any cell of your 2x2 table. Use Chi-square test when all expected cell counts are ≥5. Fisher's test provides exact p-values for small samples, while chi-square is an approximation suitable for larger samples.
How to interpret Number Needed to Treat (NNT)?
NNT represents how many patients need to be treated to prevent one adverse outcome. Lower NNT values indicate more effective treatments. NNT = 1/ARR (absolute risk reduction). For example, NNT = 5 means treating 5 patients prevents 1 adverse event.

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