While all might not agree that those were the only causes, or that the greatest areas of wheat farming suffered the worst drought and dust storms, there was a causal relationship. Plowed land is a much greater source of blowing dust than uncultivated grassland. Humans responded to the problems of the 1930s. Those who remained changed their farming techniques between the 1930s and 1970s. The data used in this project came at a variety of scales, and these have a strong influence on the research.
Demographic data constitute the primary source for much of the analysis.
While there are many kinds of demographic data available, population census data constitute the most important source in this work. The U. S. population census data are published at higher levels of aggregation than the individual, such as the city, county, metropolitan area, or state. The smallest levels of aggregation for which there are published data for recent censuses are the block, block group, or census tract. A block group is a cluster of blocks having the same first digit of their three-digit identifying numbers within a census tract. There are few data at levels smaller than the county before 1940.