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Standard Deviation Charts
Standard deviation charts provide a visual representation of the data in the SD list. To display an SD chart, put the calculator into the Standard Deviation mode, and then select a suitable chart, i.e. a histogram, from the Chart->SD Data Charts menu.
Histogram
A histogram shows the frequency distribution as a series of bars, where each bar represents an interval in the value data range. You can select the number of classes (bars) or have DreamCalc determine a suitable number using Scott's Rule by selecting "Auto" from the drop-down list.
An example histogram and cumulative variation are shown below:
Histogram Chart
Cumulative Histogram Chart
A cumulative chart can be shown for both histograms and frequency polygons. In addition, the axes may be set to show relative values. These settings can be found under the Chart Windows Axes menu; for example, select Axes->Cumulative Chart.
In addition, you can use the Show Normal Distribution option under the Chart->SD Data Charts menu to toggle a Gaussian curve fit to the underlying data.
Frequency Polygon
The frequency polygon chart is similar to a histogram (above), but shows the frequency distribution as a single line rather than a series of bars.
Bar Chart
The bar chart displays values as a bars, in the order the they are listed, with bar widths proportional the corresponding frequencies.
Normal Q-Q Plot
Professional Edition Only. A Normal Quantile-Quantile (Q-Q) plot is a graphical technique used to determine whether the data is normally distributed.
An example Q-Q Plot is shown below:
Normal Quantile-Quantile Plot
The x-axis shows the values in SD list, while the y-axis shows the expected corresponding values of a normal distribution with the same mean and standard deviation of the data. The closer the points lie to the 45° line, the closer the data resembles a normal distribution. A departure from the central line, for example, suggests that data is heavily tailed.
The axes of the Q-Q chart may be shown in terms of normalized variate Z values by selecting Relative Chartfrom the Axes menu.
See also: Chart & List Window, Statistical Calculations
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