Odds ratio in prognostic studies expresses what?

Odds ratio in prognostic studies expresses what?

• A. The absolute risk difference
• B. The relative risk
• C. The odds that the outcome occurs with a prognostic factor versus without
• D. The hazard ratio

Answer: (C)

The odds ratio in prognostic studies expresses how much more (or less) likely the outcome is when the prognostic factor is present compared with when it is absent, using odds rather than probabilities. In a 2x2 setup, you compare the odds of the outcome with the factor to the odds of the outcome without the factor. The odds ratio is computed as the cross-product ratio, (A × D) / (B × C), where A is the number with both factor and outcome, B is with the factor but no outcome, C is without the factor but with the outcome, and D is without the factor and without the outcome. An odds ratio greater than 1 means the factor is associated with higher odds of the outcome; less than 1 means lower odds; equal to 1 means no association. This differs from absolute risk difference (a measure of difference in probabilities) and from relative risk (a ratio of probabilities) and from time-to-event analysis captured by the hazard ratio. For example, if 40 have the factor and outcome, 10 have the factor without the outcome, 20 do not have the factor but have the outcome, and 30 do not have the factor nor the outcome, the odds ratio would be (40×30)/(10×20) = 1200/200 = 6, indicating the presence of the factor is associated with substantially higher odds of the outcome.

The odds ratio in prognostic studies expresses how much more (or less) likely the outcome is when the prognostic factor is present compared with when it is absent, using odds rather than probabilities. In a 2x2 setup, you compare the odds of the outcome with the factor to the odds of the outcome without the factor. The odds ratio is computed as the cross-product ratio, (A × D) / (B × C), where A is the number with both factor and outcome, B is with the factor but no outcome, C is without the factor but with the outcome, and D is without the factor and without the outcome. An odds ratio greater than 1 means the factor is associated with higher odds of the outcome; less than 1 means lower odds; equal to 1 means no association. This differs from absolute risk difference (a measure of difference in probabilities) and from relative risk (a ratio of probabilities) and from time-to-event analysis captured by the hazard ratio. For example, if 40 have the factor and outcome, 10 have the factor without the outcome, 20 do not have the factor but have the outcome, and 30 do not have the factor nor the outcome, the odds ratio would be (40×30)/(10×20) = 1200/200 = 6, indicating the presence of the factor is associated with substantially higher odds of the outcome.