To ensure that your results are valid, consider the following guidelines when you collect data, perform the analysis, and interpret your results.

- You must be able to count the number of defects on each item or unit
- A defect is any departure from specifications. A defect does not necessarily mean that the product or service cannot be used, just that it wasn't as intended.
- Consider a loan application process. You sample several forms to estimate the defect rate. One application has 7 incorrect entries—there are 7 defects present on this form. Another application has 4 incorrect entries—there are 4 defects present on this form.
- You must be able to count the number units
- Consider a loan application process. You sample 50 forms to estimate the defect rate. The number of units is 50.
- You must be able to count the number of opportunities per unit
- Consider a loan application process. The application form has 36 entries. The number of opportunities per unit is 36.