07 Useful Discrete Distributions & Exercise

Module 2 Probability & Reliability Statistics

Lesson M02-07

Text: Section 3 pages 30 – 40

Participant Guide: Module 2 page 54

Duration: 35 minutes

When dealing with pass/fail outcomes or count data, discrete distributions are necessary.  In this lesson, we introduce the binomial distribution which models the probability of observing a specified number of failures from a sample size, given an assumed failure probability.  In addition to directly supporting probability calculations involving inspection data, the concepts will be very useful in understanding system probability calculations later in the course.  The Poisson distribution is also covered as it’s often useful in modeling the number of defects (where a particular unit may have more than 1 defect).

Exercise Question

A supplier of integrated circuits claims that at most 5% should fail a 20-hour stress test (high relative humidity). A customer performs the same test on 30 ICs and observes 6 failures. What is the probability of observing at least 6 failures if the supplier claim is true?