The establishment of criteria for air pollutants requires that a threshold level be established below which no adverse health effects are observed. Since standard dose response curves, such as the logit or probit, assume an effect at all levels, a segmented function was developed. This function has zero slope up to a point, and then increases monotonically from that point. Thus the name hockey stick function. The increasing portion need not be linear; any function that can be fitted by least squares techniques will work. A method for computing confidence intervals is also given. Since the curve can be used as a dose response curve, some comparisons are made with the more conventional probit and logit curves. In general, the fit of the hockey stick curve is as good as either the logit or probit curve, even when the data originate from a logit or probit distribution.

"June 1976." "EPA/600-1-76-024." Includes bibliographical references (page 9).