### 15.10 ONEWAY

         ONEWAY
                 [/VARIABLES = ] var_list BY var
                 /MISSING={ANALYSIS,LISTWISE} {EXCLUDE,INCLUDE}
                 /CONTRAST= value1 [, value2] ... [,valueN]
                 /STATISTICS={DESCRIPTIVES,HOMOGENEITY}
                 /POSTHOC={BONFERRONI, GH, LSD, SCHEFFE, SIDAK, TUKEY, ALPHA ([value])}

The `ONEWAY` procedure performs a one-way analysis of variance of variables factored by a single independent variable. It is used to compare the means of a population divided into more than two groups.

The dependent variables to be analysed should be given in the `VARIABLES` subcommand. The list of variables must be followed by the `BY` keyword and the name of the independent (or factor) variable.

You can use the `STATISTICS` subcommand to tell pspp to display ancilliary information. The options accepted are:

- DESCRIPTIVES Displays descriptive statistics about the groups factored by the independent variable.
- HOMOGENEITY Displays the Levene test of Homogeneity of Variance for the variables and their groups.

The `CONTRAST` subcommand is used when you anticipate certain differences between the groups. The subcommand must be followed by a list of numerals which are the coefficients of the groups to be tested. The number of coefficients must correspond to the number of distinct groups (or values of the independent variable). If the total sum of the coefficients are not zero, then pspp will display a warning, but will proceed with the analysis. The `CONTRAST` subcommand may be given up to 10 times in order to specify different contrast tests. The `MISSING` subcommand defines how missing values are handled. If `LISTWISE` is specified then cases which have missing values for the independent variable or any dependent variable will be ignored. If `ANALYSIS` is specified, then cases will be ignored if the independent variable is missing or if the dependent variable currently being analysed is missing. The default is `ANALYSIS`. A setting of `EXCLUDE` means that variables whose values are user-missing are to be excluded from the analysis. A setting of `INCLUDE` means they are to be included. The default is `EXCLUDE`.

Using the `POSTHOC` subcommand you can perform multiple pairwise comparisons on the data. The following comparison methods are available:

- `LSD` Least Significant Difference.
- `TUKEY` Tukey Honestly Significant Difference.
- `BONFERRONI` Bonferroni test.
- `SCHEFFE` Scheffé's test.
- `SIDAK` Sidak test.
- `GH` The Games-Howell test.

The optional syntax `ALPHA(`value`)` is used to indicate that value should be used as the confidence level for which the posthoc tests will be performed. The default is 0.05.