Review Descriptive Statistics - Advanced Tab

Select the Advanced tab of the Review Descriptive Statistics dialog box to access the options described here.

Means & standard deviations. Click the Means & standard deviations button to display a spreadsheet with means and standard deviations for all items in the scale. By default the standard deviation is computed as the square root of the sum of squared deviations about the mean (SS) divided by N - 1. The resulting statistic is an estimate of the population Sigma (this statistic can then be used to draw inferences about the population from which the sample was drawn). You can select the SD=Sums of Squares/N check box to compute the standard deviation as the SS divided by N.

A useful Graph of Input Data for this spreadsheet is a histogram (frequency distribution) of the selected variable, with the normal distribution superimposed. This plot can be beneficial as a quick check of whether the assumption of normality has been violated (on which the computation of the correlation coefficients is based, see Correlations - Introductory Overview).

Correlations. Click the Correlations button to display either tetrachoric correlations or Pearson-product moment correlations, according to the Correlation matrix selected via the Reliability and Item Analysis - Advanced tab. A useful Graph of Input Data for this spreadsheet is a scatterplot of the respective correlation coefficients. The plot will indicate the regression line as well as the 95% confidence limits for the regression line.

Covariances. Click the Covariances button to display a spreadsheet with the covariance matrix for all items in the scale. A useful Graph of Input Data for this spreadsheet is a scatterplot of the selected variables. The plot will indicate the regression line as well as the 95% confidence limits for the regression line.

Box & whisker plot. Click the Box & whisker plot button, select the variables you wish to plot via the standard variable selection dialog, and select an option from the Box-Whisker Type dialog box to produce a box and whisker plot. For details concerning the median and the quartiles, refer to the Computation of percentiles option in the Options dialog box - Analyses/Graphs: Limits tab (accessible by selecting Options from the Tools menu). For more information, see Percentile Calculation Options in STATISTICA.

Scatterplot matrix. Click the Scatterplot matrix button to display the standard variable selection dialog, in which you select the variables you wish to plot. Click the OK button to display a matrix scatterplot for the selected variables.

SD=Sqrt(SS/N). Select the Sqrt(SS/N) check box to compute the standard deviation as the square root of the sums of squares divided by number observations. There are two ways in which standard deviations can be computed: as the square root of sums of (deviation) squares divided by N (the valid number of cases) or N-1. If divided by N-1, the resulting standard deviations are estimates of the standard deviations in the population (Sigma); if divided by N, the resulting standard deviations are descriptions of the sample only. The setting of this check box will not affect the subsequent computations of the reliability coefficients.