Non-response is a serious threat to the external validity of longitudinal psychosocial studies. Little is known about potential systematic differences between patients with coronary artery disease who complete a psychosocial study and those who drop out prematurely due to non-response, or whether drop-outs may have a different cardiovascular risk. We studied a cohort of 1132 consecutive patients undergoing percutaneous coronary intervention (PCI). At baseline, all patients completed the Hospital Anxiety and Depression Scale (HADS) and the Type D Scale (DS14). At 12 months follow-up, 70.8% (n = 802) of patients completed both questionnaires, while 29.2% (n = 330) dropped out. We observed significant differences in socio-demographic, clinical, and psychological baseline characteristics between completers and drop-outs. Drop-outs were younger, more likely to smoke, but less often prescribed cardiovascular medications, including calcium antagonists and angiotensin-converting enzyme inhibitors, as compared with completers. Drop-outs more often had depression, anxiety, and negative affectivity, as compared with completers (all p-values <0.05). After a median follow-up of 4 years, we found no significant differences in mortality risk between completers and drop-outs (6.5 vs. 7.3%; adjusted HR 1.34, 95% CI 0.82–2.19, respectively). In conclusion, a possible attrition bias occurred, as drop-outs and completers differed systematically on some socio-demographic, clinical, and psychological baseline characteristics. Despite these differences, this did not translate into a poorer short-term prognosis, as there were no differences in the mortality risk of completers vs. drop-outs after a median follow-up of 4 years. In future prospective studies, attention should be paid to attrition bias, and its possible impact on study results and implications should be discussed.
Damen, N. L. M., Versteeg, H., Serruys, P. W., van Geuns, R-JM., van Domburg, R. T., Pedersen, S. S., & Boersma, E. (2015). Cardiac patients who completed a longitudinal psychosocial study had a different clinical and psychosocial baseline profile than patients who dropped out prematurely. European Journal of Preventive Cardiology, 22(2), 196-199. https://doi.org/10.1177/2047487313506548