Abstract
Regression relations are sometimes better expressed by two intersecting straight lines than by a single line; for example a sudden change in internal or external conditions may alter the rate of linear growth of an organism. Tests are developed to determine i) whether a change in slope occurs at a specified value of the independent variate and ii) whether the change in slope occurs at the same value of the independent variate for a number of two-phase regressions, subject to parallelism within each phase. Fiducial limits and extension to other cases are briefly discussed. A numerical example is given, based upon a study of fruit bud development.

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