Reproducibility of the history of low-back trouble.

The reproducibility of auto-anamnestic information concerning low back trouble (LBT) was analyzed in 6 and 12 months' follow-up studies of a general population of 30-, 40-, 50-, and 60-year-old men and women and of a population of male hospital porters 20-68 years old. At an interval of about 6 months, the question of ever having had LBT was answered by yes/no in a ratio of approximately 2:1, and 84% answered consistently on the two occasions. Affirmative or negative answers concerning previous lumbar spine x-ray examination were contradicted at 1 year's interval by 11%. After 6 months, two-fifths of the subjects reproduced their statement of age at onset of LBT +/- 1 year. The cumulative incidence curves of LBT estimated by age at onset varied systematically between the 30 years old and the 60 years old, suggesting forgetful behavior. The annual risk of first time experience of LBT was seemingly about fourfold higher during the follow-up year than during the 7 preceding years. This feature also can be explained by forgetfulness. The caution with which data obtained by means of subjective statements should be handled is stressed, together with the significant influence that different methods of data collection tend to have on the results.