## Regression--comparing trends from different treatments.Note: this page documents an arrangement of treatments rather than an experimental design. The design used in the examples is a CRD.
- A set of levels from a continuous range (quantitative difference) are crossed on treatments with qualitative differences. For example, amount of fertilizer crossed on method of application
5Aa 2Aa 5Ba 5Ab 2Ba 1Ba 1Bb 1Aa 2Bb 2Ab 1Bc 1Ab 5Ac 2Bc 2Ac 1Ac 5Bb 5Bc 1Ad 5Bd 5Ad 1Bd 2Bd 2Ad
Note: in this example, the regression line intercepts (Treatment) are significantly different and the common slope (Regression) is different than zero, but the different slopes (Treatment X Regression) are not different.
PROC GLM; CLASS TREAT; MODEL Y = TREAT X TREAT*X / SOLUTION; LSMEANS TREAT; RUN; Note: the SOLUTION option returns the regression line parameters. LSMEANS returns the treatment means adjusted for the regression.
- Two-way Factorial arrangement on a CRD: Treatments are combinations of two qualitative sets.
- Regression--treatments from a continuous range Treatments are from a single continuous range.
- Analysis of covariance--controlling variation with a second measureable factor additional variation is controlled by measuring a second variable on each subject.
- RCB repeated in time: one set of treatments is examined at different times.
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