DERIVING DICHOTOMOUS OUTCOME MEASURES FROM CONTINUOUS DATA IN RANDOMIZED CONTROLLED TRIALS OF ANALGESICS - USE OF PAIN INTENSITY AND VISUALANALOG SCALES

The aim of this study was to examine whether mean data from categorica l pain intensity and visual analogue scales for both pain intensity an d relief could be used reliably to derive dichotomous outcome measures for meta-analysis. Individual patient data from randomised controlled trials of single-dose analgesics in acute postoperative pain were use d. The methods used were as follows: data from 132 treatments with ove r 4700 patients were used to calculate mean %maxSPID (categorical pain intensity), %maxVAS-SPID (visual analogue pain intensity) and %maxVAS -TOTPAR (visual analogue pain relief); these were used to derive relat ionships with the number of patients who achieved at least 50% pain re lief (%maxTOTPAR). Good agreement was obtained between the actual numb er of patients with >50%maxTOTPAR and the number calculated for all th ree measures. For SPID, verification included independent data sets. F or calculations involving each measure, summing the positive and negat ive differences between actual and calculated numbers of patients with >50%maxTOTPAR gave an average difference of less than 0.25 patients p er treatment arm. Reports of randomised trials of analgesics frequentl y describe results of studies in the form of mean derived indices, rat her than using discontinuous events, such as number or proportion of p atients obtaining at least 50% pain relief. Because mean data inadequa tely describe information with a nonnormal distribution, combining suc h mean data in systematic reviews may compromise the results. Showing that dichotomous data can reliably be derived from mean SPID, VAS-SPID and VAS-TOTPAR as well as TOTPAR data in previously published acute p ain studies makes much more information accessible for meta-analysis.