How to create p- or np-chart
This help page describes how you can create p- or np-chart in Power BI, using the Craydec Control Charts.
What are they / When to use
The p- and np-charts are used to track the number of faulty items produced by a process over time. Both charts use count data, for example number of faulty parts. Interpreting the count requires an Area of Opportunity, for example, number of parts produced.
The p- and np-charts track number of faulty items, this means that item can have one or multiple faults, it is still counted as one, ie. pass or fail. The count must also be between 0 and Area of Opportunity, as you can’t have more faulty items than the number of items you produce.
The difference between the p- and np-chart is that np-chart has fixed Area of Opportunity, and p-chart has variable AoO.
The np-chart has single limits because it has fixed Area Of Opportunity.
Creating np-chart
Data required
x, count
Example data. This data is used in the downloadable example report.
id = x, number_faulty_items = measured value
Steps
1) Add visual to the report
See the Microsoft’s documentation.
2) Prepare data
See the Microsoft’s documentation.
Note that count must be numeric data type, usually a whole number. X can be number, text, or date, but it must sort the data correctly. It is also good idea to have unique values for x in each row, unless ‘Row ID’ is used.
3) Add data roles
Select data roles. As order of the data lines is crucial for the correct visualization, it is safest to start by selecting ‘id’ or ‘x’ data role first.
4) Enter a license code
See the help video.
5) Change chart type
Select Format > Chart > Chart Type > ‘np-chart’. You have to have a valid license to change the chart type.
6) Select AoO size
The np-chart must have a fixed size Area of Opportunity. Enter the size of the AoO in Format > Chart > ‘n / Area of Opportunity’. The default value is 100.
7) Check results
Common errors
See separate common errors page.
Examples
See the example report. Data contains fictional set of count of faulty items produced by a process. The Area of Opportunity is 60.
Creating p-chart
Data required
x, count, area of opportunity
Example data. This data is used in the downloadable example report.
id = x, number_faulty_items = measured value, area_of_opportunity = Area of Opportunity
Steps
1) Add visual to the report
See the Microsoft’s documentation.
2) Prepare data
See the Microsoft’s documentation.
Note that count and area of opportunity must be numeric data type, usually a whole number. X can be number, text, or date, but it must sort the data correctly. It is also good idea to have unique values for x in each row, unless ‘Row ID’ is used.
3) Add data roles
Select data roles. As order of the data lines is crucial for the correct visualization, it is safest to start by selecting ‘id’ or ‘x’ data role first.
4) Enter a license code
See the help video.
5) Change chart type
Select Format > Chart > Chart Type > ‘p-chart’. You have to have a valid license to change the chart type.
6) Check results
Note that p-chart must relate the count to the area of opportunity, so the result is shown as rate. This is a feature of a p-chart, and it cannot be avoided.
Common errors
See separate common errors page.
Examples
See the example report. Data contains fictional set of count of faulty items produced by a process.