Tick marks are drawn uniformly across the axis based on the quantile scale. If the data are from the theoretical distribution, the points on the QQ plot lie approximately on a straight line. I usually assess the distribution of my data using these three tools: Specifies maximum number of iterations in the Newton-Raphson approximation of. For the normal distribution, the i th ordered observation is plotted against the normal quantile ,where is the inverse standard cumulative normal distribution. Further information on interpreting quantile-quantile plots can be found in Chambers et al.

An advantage of the two-parameter Weibull plot over the three-parameter Weibull plot is that the parameters c and can be estimated from the slope and intercept of the point pattern. Agreement between the reference line and the point pattern indicates that the lognormal distribution with parameters , , and is a good fit. Version Base SAS 9. Specifies a two-parameter Weibull Q-Q plot. Specifies mandatory shape parameter. The distributions available are the beta, exponential, gamma, lognormal, normal, two-parameter Weibull, and three-parameter Weibull. Specify these options in parentheses after the distribution keyword.

### PROC CAPABILITY: Estimating Parameters from Lognormal Plots –

Q-Q plots are preferable for graphical estimation of distribution parameters, whereas probability plots are preferable for graphical estimation of percentiles. For more information, see the sq Generalized Pareto Distribution. You can specify only one option that names the distribution in each QQPLOT statement, but you can specify any number of other options.

For more information, see the section Normal Distribution. If the data distribution matches the theoretical distribution, the points on the plot form a linear pattern.

By default, the procedure produces a plot for the normal distribution. Because the point pattern is curved with slope increasing from left to right, a theoretical distribution that is skewed to the right, such as a lognormal distribution, should provide a better fit than the normal distribution. An advantage of the two-parameter Weibull plot over the three-parameter Weibull plot is that the parameters c and can be estimated from the slope and intercept of the point pattern.

This option also creates a grid if the GRID option is not specified. Agreement between the reference line and the point pattern indicates that the lognormal distribution with parameters, and is a good fit. The following statements create the series of plots in Output 5.

## QQPLOT Statement: CAPABILITY Procedure

See the section Normal Distribution for details, and see Example 4. Specifies for distribution reference line. You can then estimate the threshold and scale parameters from the intercept and slope of the point sws.

See the section Exponential Distribution for details. The th percentile of the lognormal distribution is. The result is shown in Output 5. Options can be any of the following: If the data distribution matches the theoretical distribution, the points on the plot form a plor pattern. The option does not apply to ODS Graphics output. Agreement between the reference line and the point pattern indicates that the generalized Pareto distribution with parameters, and kognormal a good fit.

The th percentile is 5. Agreement between the reference line and the point pattern indicates that the exponential distribution with parameters and is a good fit.

Therefore, you should familiarize yourself with the different tools available for distribution fitting. For more information, see the section Gamma Distribution. See the section Distributions for Probability and Q-Q Plots for detailed descriptions of these distributions.

Here though, the syntax does not allow me to request these in a single statement. For detailed descriptions of these distributions, see the section Distributions for Probability and Q-Q Plots.

Thus, you can use a Q-Q plot to determine how well a theoretical distribution models a set of measurements. See the section Gamma Distribution for details. In the dialog, you must specify a shape parameter for the lognormal or Weibull distribution.

If the data are from the theoretical distribution, the points on the QQ plot lie approximately on a straight line. You can specify the following axis-options: These values correspond to the previous estimates of for and for. Goodness of Fit tests are statistical sizes that quantify how well some distribution fits your data.

By default, the procedure produces lognormla plot for the normal distribution. For the exponential distribution, the i th ordered observation is plotted against the exponential quantile -log 1- v i.