Descriptive Statistics

We can replicate the frequency analyses that are described in chapter 2 of the text, by using the file that was just read into the data editor - tab2-1.dat. These analyses were conducted on the reaction time data. Recall, that we have labelled this data as RT.

To begin, click on [Statistics=>Summarize=>Frequencies]....

The result is a new dialog box that allows the user to select the variables of interest. Also, note the other clickable buttons along the border of the dialog box. The buttons labelled [Statistics...] and [Charts...] are of particular importance. Since we're interested in the reaction time data, click on rt followed by a mouse click on the arrow pointing right. The consequence of this action is a transference of the rt variable to the Variables list. At this point, clicking on the [OK] button would spawn an output window with the Frequency information for each of the reaction times. However, more information can be gathered by exploring the options offered by the [Statistics...] and [Charts...].

[Statistics...] offers a number of summary statistics. Any statistic that is selected will be summarized in the output window.

As for the options under [Charts...] click on Bar Charts to replicate the graph in the text.

Once the options have been selected, click on [OK] to run the procedure. The results are then displayed in an output window. In this particular instance the window will include summary statistics for the variable RT, the frequency distribution, and the frequency distribution. You can see all of this by scrolling down the window. The results should also be identical to those in the text.

You may have gathered from the above that calculating summary statistics requires nothing more than selecting variables, and then selecting the desired statistics. The frequency example allowed us to generate frequency information plus measures of central tendencies and dispersion. These statistics can be had by clicking directly on [Statistics=>Summarize=>Descriptives]. Not surprisingly, another dialog box is attached to this procedure. To control the type of statistics produced, click on the [Options...] button. Once again, the options include the typical measures of central tendency and dispersion.

Each time as statistical procedure is run, like [Frequencies...] and [Descriptives...] the results are posted to an Output Window. If several procedures are run during one session the results will be appended to the same window. However, greater organization can be reached by opening new Output windows before running each procedure - [File=>New=>Output]. Further, the contents of each of these windows can be saved for later review, or in the case of charts saved to be later included in formattted documents. [Explore by left mouse clicking on any of the output objects (e.g., a frequency table, a chart, ...) followed by a right button click. The left left button click will highlight the desired object, while the right button click will popup a new menu. The next step is to click on the copy option. This action will store the object on the clipboard so that it can be pasted to Word for Windows document, for example.....]