Overview of Power and Sample Size .com Calculators

We have 30 calculators. This is a quick-start guide.

Usage Instructions

These calculators should be mostly self-explanatory. Just a few quick points here.

Each calculator's page has two main sections. The calculator and output are at the top, further information and the menu are on the bottom half of the page.

When you first view the calculator, it's form it is pre-filled with values. You may fill in the form with whatever values you like ... with obvious restrictions such as numbers must not contain text, variances must be positive, probabilities must be between 0 and 1, etc.

All inputs are required, except of course sample size, which is at the top of the form, and displays the calculated sample size required for the given input values. After filling in the input values, click the button at the bottom of the form to see the new sample size and graph.

The calculators always round up the calculated sample size to the nearest whole number, which may create a "step" pattern in the graph.

The graph is intended to provide you with a nice visual aid of how sensitive the required sample size is to the input parameter values. The y-axis (vertical) of the graph is always sample size, and the x-axis (horizontal) can be chosen with the drop-down menu below the graph. You may adjust the range of the x-axis in two ways: use the slider under the graph; enter values in the "min" and "max" boxes and then hit "resize".

Currently, the graph will always display 2 or 3 curves, each one representing the sample-size curve for different choices of power. The legend above the graph identifies which curve goes with which power level. As you mouse-over the graph the legend will show the calculated sample size and x-value as you move the mouse over the graph.

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