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.
Suppose you sample application 50 forms and find that 18 forms have at least one defect. You count the total number of defects and find 62. The number of units is 50. The total number of opportunities is 1800 opportunities (36 opportunities per form * 50 forms).