Feedback Form for WebCT Students: Click icon to the left for a form on which you can record your understanding of this material. (Password protected.) For further reading, we suggest "The Declining Middle," an essay in the Atlantic Monthly by Bob Kuttner. Kuttner's 1983 essay analyzes the effects of various economic changes in American life. (It is interesting to see, now, how much of what he said about these effects has come to be true.) For a lengthy and complex article that defines the causes of homosexuality, read Chandler Burr's "Homosexuality and Biology." Burr's article ( Atlantic , 1997) is also an excellent example of an essay that defines .
For nonexperimental data, causal direction can often be inferred if information about time is available. This is because (according to many, though not all, theories) causes must precede their effects temporally. This can be determined by statistical time series models, for instance, or with a statistical test based on the idea of Granger causality , or by direct experimental manipulation. The use of temporal data can permit statistical tests of a pre-existing theory of causal direction. For instance, our degree of confidence in the direction and nature of causality is much greater when supported by cross-correlations , ARIMA models, or cross-spectral analysis using vector time series data than by cross-sectional data .