This can be used to display a probability plot for variables.
1. Choose ProcessMA > Graphs > Probability Plot.
2. In Variable, select the column containing variable data.
3. In Distribution, select the distributions to fit.
4. In Historical parameters, enter historical estimates of the distribution parameters.
5. Check Show confidence level, to plot confidence interval.
6. In Confidence level, enter a confidence level for the confidence intervals.
7. Click OK.
Note To select a column of data into a textbox, double-click on any of the column names shown in the list on the left of the dialog box while in the textbox.
Variable: Numeric.
Historical parameters: Numeric.
Confidence level: Numeric; Between 0 to 100.
You work in a manufacturing plant making widgets and you collected failure times for 50 widgets. You want to determine if a Normal distribution fits your data.
1. Open worksheet ProcessMA > Tools > Data Files > Reliability.xls.
2. Choose ProcessMA > Graph > Probability Plot.
3. In Variable, select A – Failure Times.
4. In Distribution, select Normal.
5. Click OK.
Interpretation
The data fits a normal distribution with mean of 161.6 and standard deviation of 21.527 fairly well.