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Contradictory correlations between derived scales
Author(s) -
Thompson M. J.,
Hand D. J.,
Everitt B. S.
Publication year - 1991
Publication title -
statistics in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.996
H-Index - 183
eISSN - 1097-0258
pISSN - 0277-6715
DOI - 10.1002/sim.4780100815
Subject(s) - correlation , pain relief , duration (music) , pain scale , scale (ratio) , medicine , statistics , physical therapy , mathematics , anesthesia , physics , cartography , geography , geometry , acoustics
In a clinical trial one scale of pain relief is scored backwards relative to another (high on one corresponding to low on the other), with a consequent large negative correlation. But two derived scales of total pain, obtained by multiplying average pain relief on each scale by duration of pain (common to both pain relief measurements) gave an almost zero correlation. This apparent contradiction is explained by the inverse relationship between the pain relief scales and the large differences in duration of pain experienced by the patients.