Compute and Visualize Results for an ANCOVA Model

Fit data to an analysis of covariance model, extract the ANOVA table and visualize the level curves for the four treatment groups.

In[1]:=

groups = {"control", "treatment 1", "treatment 2", "treatment 3"};

data = BlockRandom[SeedRandom[123];

   Block[{vals, times, rand},

    vals = RandomChoice[groups, 100];

    times = RandomInteger[10, 100];

    rand = RandomReal[1, 100];

    Transpose[{vals, 

      times, (vals /. 

         Thread[Rule[groups, {.16, .34, .57, 1.1}]]) - .05 times + 

       rand}]]];

In[2]:=

lm = LinearModelFit[data, {treatment, time}, {treatment, time}, 

   NominalVariables -> treatment];

Grid[{{lm["ANOVATable"]}, {Show[

    ListPlot[Drop[GatherBy[Sort[data], First], None, None, 1], 

     PlotRange -> All], 

    Plot[Evaluate[Map[lm[#, t] &, groups]], {t, 0, 10}]]}}]

Out[2]=