[Validation of the questionnaire for adolescents concerning ailments of lumbosacral region. Part III: validity].

The third part of the series of articles includes the results of validity and coherence check conducted over the LBP questionnaire designed for pupils aged 13-18. 22 adolescents aged 13-17 were randomly chosen from the group of 124 pupils, who filled in the questionnaire using stratification to 3 groups: without LBP, LBP in a life time, but not in the week preceding the testing and LBP in the preceding week. The validity of questions was tested by comparison to the data obtained from parents and in clinical testing conducted by a physiotherapist, which took place within two weeks from the first questionnaire session. The questions were found valid if the answers or indexes counted from the answers were consistent with data from clinical testing and from parents. For birth date, height and weight data from parents were used. Data from clinical testing served to verify: height, weight, presence and location of pain (local symptoms of overloading were palpated), faulty posture and directional preference according to McKenzie. With reference to some questions the coherence check was performed, by comparing the answers to questions logically linked. As a result of validity and coherence check rejected were the questions about: intensive growth period (small number of answers together with many incoherent ones), about beginning of pain episode (lack of coherence), about directional preference (differences with clinical testing) and about faulty posture (not consistent with findings in clinical testing). On the other hand the question about presence of LBP proved to be highly specific, good results were also found as to the questions about birth date, height and weight. The rest of the questions tested were found acceptable.