Measurement error in direct observations: a comparison of common recording methods

Abstract

Videotapes of three brief duration, three medium duration and three long duration types of stereotyped behaviour (of eight severely retarded children) were analysed to provide a criterion record of the true percentage duration of the behaviour. The criterion record was compared with the records produced by four time-sampling methods: a whole-interval method, two partial-interval methods and a momentary time-sampling method. As predicted, the whole-interval method grossly underestimated and the partial-interval methods grossly overestimated the true percentage duration of the behaviour, except when the duration of individual responses was much longer than the observation interval. Momentary time-sampling was not an errorless method but was consistently superior to the other methods.

The implications of these findings for the detection of treatment effects by direct observations are discussed.