When using behavioral-observation methods for coding video footage, it is unknown how much time of an interaction needs to be coded to gain results that are representative for the behavior of interest. The current study examined this problem using the INTAKT, a standardized observational measure for assessing the quality of mother-child interactions. Results from coding only 10 min of each video (i.e., thin slices) were compared with results from coding the remaining parts (averaging about 40 min) of the interaction. Inter-rater agreement for the short versions taken from the beginning or the middle, but not the end of the interactions indicated satisfactory observer accuracy. Coding results did not differ between short and long video sequences, when sequences were taken from the middle of the interactions. Importantly, characteristic differences between different interactive situations were equally well represented in the short and long video sequences. Therefore, our results show that coding only 10 min of an interaction is as reliable and valid as coding full-length videos, if those short sequences are taken from the middle of an interaction. Our findings support the idea that for every method, it is necessary to individually determine the window duration that is long enough to gain results that are reliable and valid.
Keywords: Behavioral observation; INTAKT; Mother-child interaction; Reliability; Thin-slice sampling; Validity.