- By convention, this is what a 2x2 table looks like.
- Be sure to label the table correctly with exposure status on the side and disease status across the top.
- One tip I found was just draw some of these out as soon as you get your scratch paper.
- You may or may not need the totals depending on what you are trying to measure.
- Just remember to think carefully about what the question is asking. Also, don’t let a change in terms throw you. For instance, instead of sick and well, you might see died and lived.
FORMULAS:
- OR = (A/B) / (C/D)
- RR = (A / (A+B)) / (C / (C+D))
- Experimental Event Rate (EER) = a/a+b
- Control Event Rate (CER) = c/c+d
- Relative Risk Reduction (RRR) = CER-EER/CER
- Absolute Risk Reduction (ARR) = CER-EER
- Absolute Risk Increase (EER-CER)
- Number Needed to Treat (NNT) = 1/ARR
- Number Needed to Harm (NNH) = 1/ARI
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MEDCALC Statistical Calculator
