Attribute Chart

Attribute charts can be used to show information about deficiencies and defects. Attribution charts are for attribute data. This is data that can be counted, just like their name suggests. This means that the data counts the number or number of defective products per unit. Variable charts such as X or R charts can be used to measure quantities like length, weight, and height.

Attribute charts are useful for identifying where problems may be occurring in your process if they can be measured using attribute data.

Defect Vs Defective


A defect is any non-conformity that doesn’t meet customer requirements. Although a product or service might have one or more defects, it is not defective if the defect prevents the product from working.

Defects can be defined as subsets or majors of defects. They are classified based on criticality into three categories: minor, medium, and large. Non-conformity is often used to indicate defects. Dimensional differences, and failure to meet safety and functional requirements, among others, are examples of such defects.

The Poisson distribution (evaluates the rate at which defects occur in the process) is used to perform defect analysis.

1 sample Poisson rate test
2 sample Poisson rate test
C chart (for constant sample size)
u chart (for variable sample sizes)
Analysis of Poisson’s capability


A product or service with one or more defects that is unsuitable for use. A product or service that has a defect in its functionality is considered defective.

Non-conform is often used to indicate defectives. Each product or service has only two options, i.e. defective or not.

The following methods are used to perform a defective analysis based on Binomial Distribution.

1 Proportion test
2 Proportion test
p chart (for variable sample size)
np chart (for constant sampling size)
Analyse binomial capabilities

Selection of control charts

The control graph is a graph that shows how a process changes over the course of time. The control chart has a center line that represents the average, a higher line for the upper limit, and a lower line that represents the lower limit. The control limits are +-3s away from the centerline.

Control chart mapping is only possible if the control chart chosen is the right one.

Use Attribute charts

Attribute charts can be used to chart either-or conditions over time, for static sample sizes (ex. 10 samples per week) or variable sample sizes.

Six Sigma certification exams can throw curveballs about applying certain attribute charts in different situations. This is a quick guide to help you determine which chart is best for which situation.

Types of Attribute Tables

There are four types:

p charts (proportional charts)
np charts
c charts
u Charts

How to choose which Attribute Chart to Use for Defects/Defectives

If you believe that a product has a defect, the guide below will help you choose which one. The lot size is constant if the Quality inspector inspects 100 bottles of information each shift. Similar to the above, lot sizes can vary depending on how many bottles were produced in a particular shift.