Occupational ecology: An evolutionary theory of the social composition of occupations.

Abstract

What accounts for shifts in the social composition of occupational groups? I demonstrate that the previous literature concerning the sociodemographic composition of occupations fails to satisfy a set of five criteria: (1) The Theory criterion (the study must be grounded in theory); (2) The Dynamic criterion (social composition must be examined over time); (3) The Multivariate criterion (multiple sociodemographic variables must be examined); (4) The Measurement criterion (segregation measures should not be used); (5) The System criterion (all types of occupational groups should be considered). This study fulfills these criteria by adapting a general ecological theory of competition from McPherson (1983) to model the social composition of occupations over time. The model assumes that the individual's social network mediates occupational outcomes and that social network ties are homophilous; the probability that any two individuals share a network connection is a function of their similarity. As occupational groups attract new members from existing network ties, these groups develop distinct sociodemographic niches in social space (e.g. in age, education, etc.). If two groups compete for individuals with similar sociodemographic characteristics, then their niches overlap. The competitive mechanism generates three testable dynamic hypotheses about shifts in the social composition of occupational groups. The first dynamic hypothesis posits that occupations move their niches (attract new associates with different sociodemographic characteristics) in response to competitive pressures produced from niche overlap (the movement hypothesis). The second dynamic hypothesis suggests that occupations increase and decrease in diversity in response to competitive pressures at the niche edges (the diversity hypothesis). The third dynamic hypothesis predicts that competitive pressures inside the niche produce growth and decline in occupational size (the growth hypothesis). I test the hypothesis with the Current Population Survey Annual Demographic Files, 1972-1989. I examine changes in movement, dispersion, and size in unidimensional social space (age and education), and multidimensional social space (age-race, age-sex, education-race, education-sex, and age-education for movement and dispersion only). I test the model in two separate time series (1972-1982 and 1983-1989), using two different occupational classification schemes. The data strongly support the movement and growth hypotheses.