# Test individual slope for each factor level in ANCOVA

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## Test individual slope for each factor level in ANCOVA

 Hi all,    Consider the data set where there are a continuous response variable, a continuous predictor "weeks" and a categorical variable "region" with five levels "a", "b", "c", "d", "e".   I fit the ANCOVA model as follows. Here the reference level is region "a" and there are 4 dummy variables. The interaction terms (in red below) represent the slope difference between each region and  the baseline region "a" and the corresponding p-value is for testing whether this slope difference is zero. Is there a way to directly test whether the slope corresponding to each individual factor level is 0 or not, instead of testing the slope difference from the baseline level?   Thanks very much.       Hanna > mod <- lm(response ~ weeks*region,data)> summary(mod) Call: lm(formula = response ~ weeks * region, data = data) Residuals:      Min       1Q   Median       3Q      Max -0.19228 -0.07433 -0.01283  0.04439  0.24544 Coefficients:                 Estimate Std. Error t value Pr(>|t|) (Intercept)    1.2105556  0.0954567  12.682  1.2e-14 *** weeks         -0.0213333  0.0147293  -1.448    0.156 regionb       -0.0257778  0.1349962  -0.191    0.850 regionc       -0.0344444  0.1349962  -0.255    0.800 regiond       -0.0754444  0.1349962  -0.559    0.580 regione       -0.1482222  0.1349962  -1.098    0.280    weeks:regionb -0.0007222  0.0208304  -0.035    0.973 weeks:regionc -0.0017778  0.0208304  -0.085    0.932 weeks:regiond  0.0030000  0.0208304   0.144    0.886 weeks:regione  0.0301667  0.0208304   1.448    0.156    --- Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 0.1082 on 35 degrees of freedom Multiple R-squared:  0.2678, Adjusted R-squared:  0.07946 F-statistic: 1.422 on 9 and 35 DF,  p-value: 0.2165         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.