These are described in detail in the next sections. They are designed to provide dynamic demonstrations of the selected probability distributions. The basic principles involved in using them is to type in the parameters you wish to use, then drag the sliding control to watch the consequent alterations in probability results. To make this more visually obvious, click the Show Graph check box at bottom right (shortcut Command-S) to see the actual probability graph, and the shaded area under it representing the probability value. Dragging the sliding bar control will also dynamically alter the area under the curve. Once you have clicked in the sliding bar control, you can drag over the graph rectangle to left and right and the graphs will continue to update, ie you do not need to keep your mouse just within the sliding bar.
You can usually alter the probability calculated ie. the shaded area under the graph. The equation specifying the meaning of the shaded area, eg. "Pr[N < z]" in the normal probability, is a pop-up button with other options for the probability calculated, and will alter the area shaded under the plot. Even the top and tail values or between these can be shown for some (normal and t-distributions). For discrete distributions, where steps in probability occur, you can specify the probability at that value alone, or above it, or below it with or without the value's probability contribution also. It is easiest to experiment with the plot showing.
A Store Graph button is provided on each Active Table after you have checked the Show Graph check box, and a graph has been drawn. Clicking this will drawn the same plot (for the current settings) in the Graph window (using the full scale of that window). You can store multiple graphs in this way. They will be layered on top of each other and can be separated by dragging them down and to the right sequentially.
Graph flicker: if the probability plot graph flickers each time you adjust it, then SchoolStat‚Ñ¢ is plotting the graphs under low memory conditions. This usually happens when you are running in 8 bit or higher color modes. To overcome this, you must increase the memory partition for SchoolStat‚Ñ¢ by quitting SchoolStat‚Ñ¢, selecting its application icon in the Finder, choosing the File menu's Get Info item, and adding to the memory used field at the bottom. If you are running on an 8 bit deep monitor, then add 70K, but for a 24 bit monitor you must add 210K to the default value. This should get rid of the flicker.
