Outcomes and estimation
Item 17a - For each primary and secondary outcome, results for each group, and the estimated effect size and its precision (such as 95% confidence interval)
Examples
Table 5 - Example of reporting of summary results for each study group (binary outcomes)*
(Adpated from table 2 of Mease et al(103))
| Endpoint | Number (%) | Risk difference (95% CI) | |
|---|---|---|---|
| Etanercept (n=30) | Placebo (n=30) | ||
| Primary endpoint | |||
| Achieved PsARC at 12 weeks | 26 (87) | 7 (23) | 63% (44 to 83) |
| Secondary endpoint | |||
| Proportion of patients meeting ACR criteria: | |||
| ACR20 | 22 (73) | 4 (13) | 60% (40 to 80) |
| ACR50 | 15 (50) | 1 (3) | 47% (28 to 66) |
| ACR70 | 4 (13) | 0 (0) | 13% (1 to 26) |
*See also example for item 6a.
PsARC=psoriatic arthritis response criteria. ACR=American College of Rheumatology.
Table 6- Example of reporting of summary results for each study group (continuous outcomes)
(Adapted from table 3 of van Linschoten(234))
| Exercise therapy (n=65) | Control (n=66) | Adjusted difference* (95% CI) at 12 months | ||||
|---|---|---|---|---|---|---|
| Baseline (mean (SD)) | 12 months (mean (SD)) | Baseline (mean (SD)) | 12 months (mean (SD)) | |||
| Function score (0-100) | 64.4 (13.9) | 83.2 (14.8) | 65.9 (15.2) | 79.8 (17.5) | 4.52 (-0.73 to 9.76) | |
| Pain at rest (0-100) | 4.14 (2.3) | 1.43 (2.2) | 4.03 (2.3) | 2.61 (2.9) | -1.29 (-2.16 to -0.42) | |
| Pain on activity (0-100) | 6.32 (2.2) | 2.57 (2.9) | 5.97 (2.3) | 3.54 (3.38) | -1.19 (-2.22 to -0.16) | |
* Function score adjusted for baseline, age, and duration of symptoms.
Explanation
For each outcome, study results should be reported as a summary of the outcome in each group (for example, the number of participants with or without the event and the denominators, or the mean and standard deviation of measurements), together with the contrast between the groups, known as the effect size. For binary outcomes, the effect size could be the risk ratio (relative risk), odds ratio, or risk difference; for survival time data, it could be the hazard ratio or difference in median survival time; and for continuous data, it is usually the difference in means. Confidence intervals should be presented for the contrast between groups. A common error is the presentation of separate confidence intervals for the outcome in each group rather than for the treatment effect.(233) Trial results are often more clearly displayed in a table rather than in the text, as shown in tables 5 and 6.
For all outcomes, authors should provide a confidence interval to indicate the precision (uncertainty) of the estimate.(48) (235) A 95% confidence interval is conventional, but occasionally other levels are used. Many journals require or strongly encourage the use of confidence intervals. They are especially valuable in relation to differences that do not meet conventional statistical significance, for which they often indicate that the result does not rule out an important clinical difference. The use of confidence intervals has increased markedly in recent years, although not in all medical specialties.(233) Although P values may be provided in addition to confidence intervals, results should not be reported solely as P values.(237) (238) Results should be reported for all planned primary and secondary end points, not just for analyses that were statistically significant or “interesting.” Selective reporting within a study is a widespread and serious problem.(55) (57) In trials in which interim analyses were performed, interpretation should focus on the final results at the close of the trial, not the interim results.(239)
For both binary and survival time data, expressing the results also as the number needed to treat for benefit or harm can be helpful (see item 21).(240) (241)
Page last edited: 24 March 2010
