Characteristics associated with non-participation in a 7 day accelerometer study
Background: Cardiovascular diseases (CVD) remain a major cause of mortality worldwide. To prevent CVD enhanced physical activity is recommended. To assess levels of physical activity as accurate as possible accelerometers can be used. We investigated self-selection bias in an accelerometer study within an apparently healthy sample.
Methods: Following a cardiovascular screening and examination program (CEP) addressing healthy adults (no prior CVD, no diabetes, self-reported body mass index < 35 kg/m2), 470 participants aged 40 – 75 years were invited to participate in a 7 day accelerometer study. We used multivariate logistic regression to estimate the association between non-participation and the following characteristics of participants: Sex, age, education, smoking, setting of recruitment for the CEP (general medical practices, job agencies, health insurance), self-reported health, and objective health criteria such as cardiorespiratory fitness (measured as VO2 peak) and absolute number of cardiovascular risk factors. We considered the following cardiovascular risk factors: Elevated waist circumference (≥102 cm for males or ≥ 88 cm for females), elevated blood pressure (systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg and/or antihypertensive medication within the last 12 month), elevated triglycerides (≥200 mg/dL), reduced high-density lipoprotein cholesterol (< 40 mg/dL for males or < 50 mg/dL for females), and elevated blood glucose (HbA1c > 6.5%). Subsequently, we stratified this analysis by sex. Finally, we used logistic regression to calculate odds ratios of non-participation for each of the cardiovascular risk factors separately, stratified by sex. Models were adjusted for age, cardiorespiratory fitness, and setting of recruitment.
Results: In total, 235 participants (40.0% men) agreed to participate in the accelerometer study. Women were more likely to decline participation (AOR= 1.7, 95% CI= 1.1 – 2.8) compared to men. Stratified analyses revealed the absolute number of risk factors as predictor of non-participation for men (AOR= 1.4, 95% CI= 1.0 – 2.0), while women did not differ on any entered variables. Considering the cardiovascular risk factors separately our results show that men with elevated blood pressure were more likely to decline participation (AOR= 1.9, 95% CI= 0,96 – 3.8) compared to men with no elevated blood pressure, even though this result barely missed statistical significance (p = 0,07). Women with elevated waist circumference were less likely to decline participation (AOR= 0.6, 95% CI= 0.3 – 0.98) compared to women with no elevated waist circumference.
Conclusions: Women were more likely to decline participation in our accelerometer study. According to sex stratified analyses, men of higher cardiovascular risk were less likely to participate in the study. There is a need to develop strategies to reduce these biases.