6.) A 2020 article in JAMA reports the findings of a study that uses data from the National Health and Nutrition Examination Study (NHANES) and from vital records data to quantify the association between physical activity (measured by the average number of "steps per day" measured by accelerometer) and all-cause mortality. The following shows a portion of the abstract from this article:

The authors present the overall results with regards to different levels of adjustment via hazard ratios in the following table (Table 2):

The results in the column "Model 1" have been adjusted for biological sex only (recorded as two levels only, male and female); the results in the column titled "Model 2" have been adjusted for sex and age, and the results in the column titled "Model 3" have been adjusted for age, sex and other characteristics listed in the right side of the above graphic.

Steps per day was measured continuously, and on average participants took 9,124 steps per day (range: 2,000 - 17,600). The relationship between mortality and steps per day was estimated via Cox regression models with a continuous x1 value for the average number of daily steps, i.e.

ln(hazard at time t)=ln(?o(t))+?^1x1ln(hazard at time t)=ln(?o(t))+?^1x1

IMPORTANCE It is unclear whether the number of steps per day and the intensity of stepping are associated with lower mortality. OBJECTIVE Describe the dose-response relationship between step count and intensity and mortality. DESIGN, SETTING, AND PARTICIPANTS Representative sample of US adults aged at least 40 years in the National Health and Nutrition Examination Survey who wore an accelerometer for up to 7 days ( from 2003-2006). Mortality was ascertained through December 2015. EXPOSURES Accelerometer-measured number of steps per day and 3 step intensity measures (extended bout cadence, peak 30-minute cadence, and peak 1-minute cadence [steps/min]). Accelerometer data were based on measurements obtained during a 7-day period at baseline. MAIN OUTCOMES AND MEASURES The primary outcome was all-cause mortality. Secondary outcomes were cardiovascular disease (CVD) and cancer mortality. Hazard ratios (HRs), mortality rates, and 95% CIs were estimated using cubic splines and quartile classifications adjusting for age; sex; race/ethnicity; education; diet; smoking status; body mass index; self-reported health; mobility limitations; and diagnoses of diabetes, stroke, heart disease, heart failure, cancer, chronic bronchitis, and emphysema. RESULTS A total of 4840 participants (mean age, 56.8 years; 2435 [54%] women; 1732 [36%] individuals with obesity) wore accelerometers for a mean of 5.7 days for a mean of 14.4 hours per day. The mean number of steps per day was 9124. There were 1165 deaths over a mean 10.1 years of follow-up, including 406 CVD and 283 cancer deaths. The unadjusted incidenceTable 2. Evaluation of Confounding in the Association Between Steps per Day and All-Cause Mortality Model 1: steps per day + sex. With Increasing Adjustment for Confounding Factors in a Study of the Association of Daily Step Count Model 2: steps per day + sex + age. and Step Intensity With Mortality Among US Adults Aged at Least 40 Years Model 3: model 2 + diet quality, Hazard ratio (95% CI) race/ethnicity, body mass index, education, alcohol consumption, Steps/d Model 13 Model 2b Model 30 smoking status, diabetes, stroke, 12 000 0.09 (0.07-0.11) 0.23 (0.19-0.29) 0.35 (0.28-0.45) coronary heart disease, heart 8000 0.21 (0.18-0.24) 0.38 (0.32-0.43) 0.49 (0.44-0.55) failure, cancer, chronic bronchitis, 4000 1 [Reference] 1 [Reference] 1 [Reference] emphysema, mobility limitation, and self-reported general health