Absence of Age-Income Correlation in Ten Rural South Dakota Counties: Real Capital Outflow or Self-selection Bias?

Previous research establishes a positive correlation between age and income during the working years of 18 to 65. Survey data from the first 10 communities in a development project in South Dakota do not exhibit this correlation. Census data is examined for the 10 counties involved to determine whether the correlation is absent countywide or if self-selection bias may have produced this result. With income distributions matching their respective counties and working age distributions that do not, factors that might skew self-selection in the observed manner are examined from a life-course perspective. Often the assumption is made that small data sets from applied projects cannot yield much information of value for research purposes. Applying nonparametric tests appropriately allowed some surprises to be discovered and explained in one such small data set. Income has long been positively correlated with age (DiazGimenez, Glover, and Rios-Rull 2011) 1 , but this correlation did not appear in surveys collected from participants in 10 community book reads across South Dakota hosted by the SDSU Extension and the Political Science and Sociology departments of South Dakota State University.