Use a probit analysis to determine the effect of a stress variable on the probability of product failure. In probit analysis, you subject a product or unit to a specified level of stress and record whether or not it is able to withstand the stress (survival or failure).

Often, you want to determine the unit's tolerance, which is how high the stress level can be before a certain percentage of the units will fail. For example, you can use probit analysis to predict the velocity at which 95% of all windshields impacted by a projectile will break. Here, the stress level is the projectile velocity and the response variable is whether or not a windshield broke after being exposed to a projectile of a certain velocity.

## Data description

A manufacturer of aircraft windshields wants to investigate how well a particular windshield can withstand a projectile impact at a range of velocities. A random sample of 90 windshields was subjected to a projectile at one of eight velocities.

The measurement of interest is whether or not the windshield can withstand the projectile impact.

Data: WindshieldStress.MTW.