Interface mechanics

Layout

The dialog window consists of 4 main sections:

Top panel

is used for inputting sample sizes (or numbers of levels), and for determining whether factor levels are fixed or random.

Bottom panel

has a row for each term in the model. Here, you can vary the effect sizes and observe the power of the test of each effect at the specified effect size.

Alpha window

in the lower right-hand corner for entering the significance level of the F tests; this applies to all the tests in the dialog.

Menu bar

contains menus for help and reporting results.

If you accessed this document using the Help menu, you have an example to look at; otherwise, there is an illustration later on.

GUI elements

The sections described above contain the following graphical-user-interface (GUI) elements:

Menus

These work just like they do in other programs you run. Many of them open a view window containing information that you can subsequently copy and paste into, say, an editor.

Radio buttons

are used in the top panel to determine whether a factor's levels are fixed or random. In a replicated design, the ``Within'' error is treated as a factor and is always random.

Input windows

are for entering numbers. Click the mouse in a window to enable it for input, and type in a value. The number you type in is not actually entered into computations until you either hit the Enter key or click the mouse in some other area of the dialog window; once that is done, the powers of all the tests are updated.

Note: The rightmost windows in the bottom panel display the powers of the tests. These are output-only windows and cannot be modified by the user.

Bar-graph displays

These are scrollbar-like GUI elements that work in conjunction with their corresponding input windows. They display values and, if you click somewhere along the center line of the bar, the value of that parameter (sample size, factor levels, or effect SD) will change. You may also drag the end of a bar to obtain a continuous update. (Like the input windows, the bars for the powers of tests are output-only.)

Numerical scales

Each family of bars has a numerical scale; it will automatically change if necessary to make room for the largest value to be displayed. You may also manually change the scale range, if you wish, by clicking the mouse on some scale label and dragging it to a new position. For example, if you click at ``.8'' and drag the mouse to ``.4'', the display will be redrawn with the ``.8'' value at the new position, approximately doubling the scale range. Of course, you cannot modify the scale beyond the limits needed to display the current values.

Bugs

One thing to be aware of is that some Java implementations are buggy. In particular, the initial window may display incorrectly, hiding some of these elements or even being completely blank. You may need to resize the window to see everything. Early versions of Java (1.0.2 and earlier, Netscape 2.0, ...) have bugs that make this dialog fall completely apart, with things appearing in the wrong places. The only cure for the latter problem is to get a more up-to-date Java-capable web browser.

Of course, there may also be some bugs in the code itself, and you should report these to the author.