Analytical problems encountered in the correlation of subjective response and pavement power spectral density functions. Paper presented at the 52nd Annual Meeting of the Highway Research Board HRB, Washington, D.C., January 1973.

It is argued and demonstrated that, when human subjective response to road roughness is functionally related through multiple regression to power aspectual density frequencies of the road profile, highly unreliable estimates of frequency coefficients result. Hence, one will be misled in assuming that such roads are especially detrimental to ride. The problem, generally designated "multicollinearity" is caused by extremely high intercorrelation of many of these frequencies.