A. Moore et al., DERIVING DICHOTOMOUS OUTCOME MEASURES FROM CONTINUOUS DATA IN RANDOMIZED CONTROLLED TRIALS OF ANALGESICS, Pain, 66(2-3), 1996, pp. 229-237
Reports of RCTs of analgesics frequently describe results of studies i
n the form of mean derived indices, rather than using discontinuous ev
ents - such as number or proportion of patients with 50% pain relief.
Because mean data inadequately describe information with a non-normal
distribution, combining mean data in systematic reviews may compromise
the results. Showing that dichotomous data can reliably be derived fr
om mean data, at least in acute pain models, indicates that more meani
ngful overviews or meta-analysis may be possible. This study investiga
ted the relationship between continuous and dichotomous analgesic meas
ures in a set of individual patient data, and then used that relations
hip to derive dichotomous from continuous information in randomised co
ntrolled trials (RCTs) of analgesics. Individual patient information f
rom 13 RCTs of parallel-group and crossover design in acute postoperat
ive pain was used to calculate the percentage of the maximum possible
pain relief score (%maxTOTPAR) and the proportion of patients with gre
ater than 50% pain relief (>50%maxTOTPAR) for the different treatments
. The relationship between the measures was investigated in 45 actual
treatments and 10 000 treatments simulated using the underlying actual
distribution; 1283 patients had 45 separate treatments. Mean %maxTOTP
AR correlated with the proportion of patients with >50%maxTOTPAR (r(2)
= 0.90). The relationship calculated from all the 45 treatments predi
cted to within three patients the number of patients with more than 50
% pain relief in 42 of 45 treatments, and 98.8% of 10 000 simulated tr
eatments. For seven effective treatments, actual numbers-needed-to-tre
at (NNT) to achieve >50%maxTOTPAR compared with placebo were very simi
lar to those derived from calculated data.