15.1 DESCRIPTIVES

DESCRIPTIVES
        /VARIABLES=var_list
        /MISSING={VARIABLE,LISTWISE} {INCLUDE,NOINCLUDE}
        /FORMAT={LABELS,NOLABELS} {NOINDEX,INDEX} {LINE,SERIAL}
        /SAVE
        /STATISTICS={ALL,MEAN,SEMEAN,STDDEV,VARIANCE,KURTOSIS,
                     SKEWNESS,RANGE,MINIMUM,MAXIMUM,SUM,DEFAULT,
                     SESKEWNESS,SEKURTOSIS}
        /SORT={NONE,MEAN,SEMEAN,STDDEV,VARIANCE,KURTOSIS,SKEWNESS,
               RANGE,MINIMUM,MAXIMUM,SUM,SESKEWNESS,SEKURTOSIS,NAME}
              {A,D}

The DESCRIPTIVES procedure reads the active dataset and outputs linear descriptive statistics requested by the user. In addition, it can optionally compute Z-scores.

The VARIABLES subcommand, which is required, specifies the list of variables to be analyzed. Keyword VARIABLES is optional.

All other subcommands are optional:

The MISSING subcommand determines the handling of missing variables. If INCLUDE is set, then user-missing values are included in the calculations. If NOINCLUDE is set, which is the default, user-missing values are excluded. If VARIABLE is set, then missing values are excluded on a variable by variable basis; if LISTWISE is set, then the entire case is excluded whenever any value in that case has a system-missing or, if INCLUDE is set, user-missing value.

The FORMAT subcommand has no effect. It is accepted for backward compatibility.

The SAVE subcommand causes DESCRIPTIVES to calculate Z scores for all the specified variables. The Z scores are saved to new variables. Variable names are generated by trying first the original variable name with Z prepended and truncated to a maximum of 8 characters, then the names ZSC000 through ZSC999, STDZ00 through STDZ09, ZZZZ00 through ZZZZ09, ZQZQ00 through ZQZQ09, in that sequence. In addition, Z score variable names can be specified explicitly on VARIABLES in the variable list by enclosing them in parentheses after each variable. When Z scores are calculated, PSPP ignores TEMPORARY, treating temporary transformations as permanent.

The STATISTICS subcommand specifies the statistics to be displayed:

ALL

All of the statistics below.

MEAN

Arithmetic mean.

SEMEAN

Standard error of the mean.

STDDEV

Standard deviation.

VARIANCE

Variance.

KURTOSIS

Kurtosis and standard error of the kurtosis.

SKEWNESS

Skewness and standard error of the skewness.

RANGE

Range.

MINIMUM

Minimum value.

MAXIMUM

Maximum value.

SUM

Sum.

DEFAULT

Mean, standard deviation of the mean, minimum, maximum.

SEKURTOSIS

Standard error of the kurtosis.

SESKEWNESS

Standard error of the skewness.

The SORT subcommand specifies how the statistics should be sorted. Most of the possible values should be self-explanatory. NAME causes the statistics to be sorted by name. By default, the statistics are listed in the order that they are specified on the VARIABLES subcommand. The A and D settings request an ascending or descending sort order, respectively.

• Descriptives Example

15.1.1 Descriptives Example

The physiology.sav file contains various physiological data for a sample of persons. Running the DESCRIPTIVES command on the variables height and temperature with the default options allows one to see simple linear statistics for these two variables. In Example 15.1, these variables are specfied on the VARIABLES subcommand and the SAVE option has been used, to request that Z scores be calculated.

After the command has completed, this example runs DESCRIPTIVES again, this time on the zheight and ztemperature variables, which are the two normalized (Z-score) variables generated by the first DESCRIPTIVES command.

get file='physiology.sav'. descriptives /variables = height temperature /save. descriptives /variables = zheight ztemperature.

Example 15.1: Running two DESCRIPTIVES commands, one with the SAVE subcommand

Screenshot 15.1: The Descriptives dialog box with two variables and Z-Scores option selected

In Result 15.1, we can see that there are 40 valid data for each of the variables and no missing values. The mean average of the height and temperature is 16677.12 and 37.02 respectively. The descriptive statistics for temperature seem reasonable. However there is a very high standard deviation for height and a suspiciously low minimum. This is due to a data entry error in the data (see Identifying incorrect data).

In the second Descriptive Statistics command, one can see that the mean and standard deviation of both Z score variables is 0 and 1 respectively. All Z score statistics should have these properties since they are normalized versions of the original scores.

Mapping of Variables to Z-scores Source Target Height in millimeters Zheight Internal body temperature in degrees Celcius Ztemperature Descriptive Statistics N Mean Std Dev Minimum Maximum Height in millimeters 40 1677.12 262.87 179 1903 Internal body temperature in degrees Celcius 40 37.02 1.82 32.59 39.97 Valid N (listwise) 40 Missing N (listwise) 0 Descriptive Statistics N Mean Std Dev Minimum Maximum Z-score of Height in millimeters 40 1.93E-015 1.00 -5.70 .86 Z-score of Internal body temperature in degrees Celcius 40 1.37E-015 1.00 -2.44 1.62 Valid N (listwise) 40 Missing N (listwise) 0

Result 15.1: Descriptives statistics including two normalized variables (Z-scores)