SPOT SAMPLING AND TIME ALLOCATION STUDIES
Instantaneous spot sampling, or time sampling, was developed in behavioral psychology in the 1920s and is widely used in ethology today. In time allocation (TA) studies, which are based on time sampling, an observer appears at randomly selected places, and at randomly selected times, and records what people are doing when they are first seen (Gross 1984).
The idea behind the TA method is simple and appealing: If you sample a sufficiently large number of representative acts, you can use the percentage of times people are seen doing things (working, playing, resting, eating) as a proxy for the percentage of time they spend in those activities.
Charles Erasmus used spot sampling in his study of a Mayo Indian community in northern Mexico (1955). As Erasmus and his wife went about the village, investigating ‘‘various topics of ethnographic interest,’’ they took notes of what people were doing at the moment they encountered them. They did not use a representative sampling strategy but they were very systematic in their recording of data.
Individual charts were made for each man, woman, and child in the village, and on
those charts were noted the page numbers from the field log where the activity descriptions were to be found. These page numbers were recorded on the charts according to the hours of the day when the observations were made. Thus, the individual charts served as indexes to the field log as well as a means of making sure that equal attention was being given to all families at all hours of the day. Periodic examination of the charts showed which households and which hours of the day were being neglected, so that visits about the community could be planned to compensate for these discrepancies. (Erasmus 1955:325)
It’s difficult to top this research for sheer elegance of design and the power of the data it produced. In the 3 months from July to September 1948, the Erasmuses made about 5,000 observations on 2,500 active adults, 2,000 children, and 500 elders in the community. From those observations, Erasmus demonstrated that men in the village he studied spent about the same time at work each day as did semiskilled workers in Washington, DC. At the time, Melville Herskovits was trying to combat the racist notion that primitive and peasant peoples are lazy and unwilling to exert themselves. Herskovits’s assertion was vindicated by Erasmus’s TA research.