# Parametric Binomial Example - Demonstrate MTTF

### From ReliaWiki

*This example appears in the Life Data Analysis Reference book*.

In this example, we will use the parametric binomial method to design a test that will demonstrate hours with a 95% confidence if no failure occur during the test . We will assume a Weibull distribution with a shape parameter . We want to determine the number of units to test for hours to demonstrate this goal.

The first step in this case involves determining the value of the scale parameter from the equation. The equation for the for the Weibull distribution is:

where is the gamma function of . This can be rearranged in terms of :

Since and have been specified, it is a relatively simple matter to calculate . From this point on, the procedure is the same as the reliability demonstration example. Next, the value of is calculated as:

The last step is to substitute the appropriate values into the cumulative binomial equation. The values of , , , and have already been calculated or specified, so it merely remains to solve the binomial equation for . The value is calculated as or units, since the fractional value must be rounded up to the next integer value. This example solved in Weibull++ is shown next.

The procedure for determining the required test time proceeds in the same manner, determining from the equation, and following the previously described methodology to determine from the binomial equation with Weibull distribution.