When a behavior is monitored, it is likely to change, even if no change may be intended. This phenomenon is known as measurement reactivity. We investigated systematic changes in accelerometer-based measures over the days of monitoring as an indicator of measurement reactivity in an adult population. One hundred seventy-one participants from the general population (65% women; mean age = 55 years, range: 42-65 years) wore accelerometers for 7 consecutive days to measure sedentary behavior and physical activity (PA). Latent growth models were used (a) to investigate changes in accelerometer wear time over the measurement days and (b) to identify measurement reactivity indicated by systematic changes in sedentary time (ST), light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA). Over the measurement days, participants reduced accelerometer wear time by trend (rate of change [b] = -4.7 min/d, P = .051, Cohen's d = .38), increased ST (b = 2.4 min/d, P = .018, d = .39), and reduced LPA (b = -2.4 min/d, P = .015, d = .38). Participants did not significantly reduce MVPA (P = .537). Our data indicated that accelerometry might generate reactivity. Small effects on ST and LPA were found. Thus, the validity of accelerometer-based data on ST and LPA may be compromised. Systematic changes observed in accelerometer wear time may further bias accelerometer-based measures. MVPA seems to be less altered due to the presence of an accelerometer.

AimsTo test the efficacy of (i) computer-generated tailored letters and (ii) practitioner-delivered brief advice for smoking cessation against an assessment-only condition; and to compare both interventions directly. Design Quasirandomized controlled trial. Setting A total of 34 randomly selected general practices from a German region (participation rate 87%). Participants A total of 1499 consecutive patients aged 18-70 years with daily cigarette smoking (participation rate 80%). Interventions The tailored letters intervention group received up to three individualized personal letters. Brief advice was delivered during routine consultation by the practitioner after an onsite training session. Both interventions were based on the Transtheoretical Model of behaviour change. Measurements Self-reported point prevalence and prolonged abstinence at 6-, 12-, 18-and 24-month follow-ups. Findings Among participants completing the last follow-up, 6-month prolonged abstinence was 18.3% in the tailored letters intervention group, 14.8% in the brief advice intervention group and 10.5% in the assessment-only control group. Assuming those lost to follow-up to be smokers, the rates were 10.2%, 9.7% and 6.7%, respectively. Analyses including all follow-ups confirmed statistically significant effects of both interventions compared to assessment only. Using complete case analysis, the tailored letters intervention was significantly more effective than brief advice for 24-hour [odds ratio (OR) = 1.4; P = 0.047] but not for 7-day point prevalence abstinence (OR = 1.4; P = 0.068) for prolonged abstinence, or for alternative assumptions about participants lost to follow-up. Conclusions The study demonstrated long-term efficacy of low-cost interventions for smoking cessation in general practice. The interventions are suitable to reach entire populations of general practices and smoking patients. Computer-generated letters are a promising option to overcome barriers to provide smoking cessation counselling routinely.

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Even in a country with poor tobacco control conditions, lifetime smokers including smokers with highly unfavourable smoking behaviours strongly support smoking policies and tobacco control measures concerning penalties and advertising/promotion. These measures should be used to promote anti-smoking legislation, and strict law enforcement of these measures is expected to be accepted by all smokers. For measures that are not supported by all lifetime smokers, interventions may be useful to increase acceptability. A limitation of the present study is the absence of never-smokers as a comparison group.

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