IN ORDER TO ASSES THE EXTENT OF THE BIAS THAT EXISTS IN ECOLOGICAL CORRELATIONS CENSUS DATA FROM THE PUBLIC USE SAMPLE AND CENSUS SUMMARY, TAPES FOR THE EAST CHICAGO STANDARD CONSOLIDATED AREA WERE USED AND A COMPARISON MADE OF CORRELATION AND REGRESSION COEFFICIENTS OF THE INDIVIDUAL VERSUS TRACT LEVEL. THE ASSUMPTION OF LARGER AGGREGATE LEVEL COEFFICIENTS WAS NOT CONSISTENTLY UPHELD. ALTHOUGH FREQUENTLY AGGREGATE COEFFICIENTS WERE LARGER THAN INDIVIDUAL LEVEL COEFFICIENTS, AT BOTH TRACT AND COUNTY LEVELS, AGGREGATE COEFFICIENTS WERE OBSERVED THAT WERE SMALLER OR IDENTICAL TO INDIVIDUAL LEVEL COEFFICIENTS. A TWO-VARIABLE AGGREGATE REGRESSION EQUATION WAS ESTIMATED FOR THE PREDICTION OF CURRENT FERTILITY AT THE TRACT LEVEL. THE EQUATION WAS ACCEPTABLE SINCE THE AGGREGATE REGRESSION COEFFICIENTS WERE RELATIVELY CLOSE TO THE INDIVIDUAL LEVEL COEFFICIENTS. TABULAR DATA, NOTES, AND REFERENCES ARE INCLUDED. (AUTHOR ABSTRACT MODIFIED--MJW)