Minitab v13 - Analysis of Variance - Two-way

The Minitab Project is available. It contains the following data:

 Column N Comments IV1Code 10 Dummy codes for groups (1=0%EDC, 2=35%EDC). IV2Code 10 Dummy codes for groups (1=young, 2=older). TrialstoPA 10 Number trials to learn PA.

Since the Two-way analysis in Minitab does not give cell means, we need to get those first. Use the "Cross Tabulation..." command off of the "Stat, Tables" menu. That is:

That will take you to the following dialog box:

For the "Classification variables:", type in (or double click on) the variables that code each IV. Everything else should be blank. Then choose the "Summaries..." button which will take you to the following dialog box.

In the box for "Associated variables:", choose the variable that contains the DV scores. Then check "Means", "Standard deviations", and "N nonmissing". Click on "OK" twice and you will see the following output.

 Tabulated Statistics: IV1Code, IV2Code Rows: IV1Code Columns: IV2Code          1      2    All 1    3.600  6.000  4.800      1.140  1.581  1.814          5      5     10 2   15.600  6.400 11.000      2.881  2.608  5.497          5      5     10 All  9.600  6.200  7.900      6.653  2.044  5.098         10     10     20 Cell Contents --        trialsto:Mean                 StDev                 N

It would be helpful to plot these means, but Minitab is not particularly friendly in this regard. For the analysis, use the "Two-way..." command off of the "Stat, ANOVA" menu. That is:

It will lead to the following dialog box:

Type (or click) in the "Response" (DV) variable as well as the variables containing the codes for each factor (i.e., "Row factor:" and "Column factor:". Checking the two "Display means" boxes gives the marginal means. Actually, we already obtained these above, but they are given here with their 95% confidence intervals. The output will appear as follows:

 Two-way ANOVA: trialstoPA versus IV1Code, IV2Code Analysis of Variance for trialsto Source       DF      SS      MS      F      P IV1Code       1  192.20  192.20  40.68  0.000 IV2Code       1   57.80   57.80  12.23  0.003 Interaction   1  168.20  168.20  35.60  0.000 Error        16   75.60    4.73 Total        19  493.80                Individual 95% CI IV1Code   Mean -------+---------+---------+---------+---- 1         4.80 (-----*-----) 2        11.00                          (-----*-----)                -------+---------+---------+---------+----                    5.00      7.50     10.00     12.50                Individual 95% CI IV2Code   Mean -+---------+---------+---------+---------+ 1         9.60                       (--------*--------) 2         6.20  (--------*--------)                -+---------+---------+---------+---------+              4.80      6.40      8.00      9.60     11.20