Therapy-dependent inconsistencies in self-reported use of complementary and alternative medicine in the general population: findings from a longitudinal study.

Objective: Information on the use of complementary and alternative medicine (CAM) in the general population is often collected by means of surveys, causing the reliability of data to rely on the memory accuracy of the respondent. The objective of this study was to examine the consistency in self-reported CAM use using data from two survey waves 4 years apart.

Design: Longitudinal study.

Setting/participants: Data were obtained from the Danish Health and Morbidity Surveys. A nationally representative subsample of the individuals invited in 2013 was reinvited in 2017. In all, 2297 individuals (≥16 years) completed the self-administered questionnaire in both waves, including questions on for example, CAM use.

Main Outcome Measures: The use of six different CAM therapies (acupuncture; craniosacral therapy; faith healing and/or clairvoyance; nutritional counselling; massage; osteopathy or other manipulative therapies; reflexology) was assessed by the response categories 'Yes, within the past 12 months', 'Yes, but previously than within the past 12 months' and 'No'. For each CAM therapy, an inconsistent response was defined as either the response combination (1) 'Yes, within the past 12 months' in 2013 and 'No' in 2017, or (2) 'Yes, within the past 12 months' or 'Yes, but previously than within the past 12 months' in 2013 and 'No' in 2017.

Results: The inconsistency percentages varied across CAM therapies. The highest levels of inconsistency for CAM use within the past 12 months were observed for nutritional counselling (64.9 %) and faith healing and/or clairvoyance (36.4 %). The lowest proportion of inconsistent responses was observed for acupuncture (18.3%). Overall, the same pattern was observed for lifetime CAM use.

Conclusions: The results highlight the difficulty in obtaining reliable prevalence estimates on the use of CAM in the general population. Future studies should take these findings into account when interpreting similar analyses.