Visual Inspection for Determining Days When Accelerometer Is Worn: Is This Valid?

Logs have been traditionally used for ascertaining accelerometer wear days in mail study designs, but not all participants complete logs. Visual inspection of accelerometer output may supplement missing logs; however, no data on the validity of this method are available.

We compared visual inspection with participant logs in 197 women (mean age, 71.0 yr). Women were mailed an accelerometer to be worn during waking hours for 7 d, marking each wear day on a log before returning the accelerometer by mail. For every participant, we created a series of graphs of accelerometer counts by time of day (one chart for each day with accelerometer output, including mail days). Two raters, masked to log wear status, independently inspected these graphs and scored each day as "worn" or "not worn."

The median (interquartile range) number of valid wear days using either visual inspection or log was 7 (7-7). For rater 1, the sensitivity and specificity of visual inspection was 99.7% (95% confidence interval, 99.2%-99.9%) and 97.2% (95.2%-98.6%), respectively; for rater 2, the sensitivity and specificity of visual inspection was 99.7% (99.2%-99.9%) and 97.0% (94.9%-98.4%), respectively. Interrater agreement was 99.5%.

Visual inspection of accelerometer data is a valid alternative to missing participant wear logs when determining wear days in mail study designs.