Other methods that do not rely on self-reported data include mechanical devices, such as light loggers. Respondents may have some difficulty knowing how many hours each light in the household is used. They may not be home during all of the times that lights are turned on and, even if home, may not know how others in the household are using lights. These findings may lead one to believe that RECS overestimates the amount of electricity used for lighting. They are not based upon light loggers or submetering.
Lighting is one of the categories.
The tendency of respondents to overestimate how long lights are on is reflected in the coefficients estimated by the regression procedure.