Template:Using contour plots

Using Contour Plots
To determine whether two data sets are significantly different and at what confidence level, one can utilize the contour plots provided in Weibull++. By overlaying two contour plots from two different data sets (analyzed using the same distribution) at the same confidence level, one can visually assess whether the data sets are significantly different at that confidence level if there is no overlap on the contours. The disadvantage of this method is that the same distribution must be fitted to both data sets.

Example 1:

Critical Confidence Level

The Critical Confidence Level utility is located as an option in the Overlay Contour Plot Setup window. To activate the utility, check the “Plot Critical Level” box as shown in the figure below.



The critical confidence level utility determines the confidence level at which the contour plots of two data sets meet at a single point. This is the minimum confidence level at which the contour plots of the two different data sets overlap. At any confidence level below this minimum confidence level, the contour plots of the two data sets will not overlap and there will be a statistically significant difference between the two populations at that level. For the two data sets in the above Example 2, the critical confidence level 94.243%. This can be seen in the figure below.



The above plot shows the contour plot at confidence level of 90% and at the critical level of 94.243%. Please notice that due to the calculation resolution and plot precision, sometimes at the calculated critical level, the two curves may look still having a little bit of overlap or separation.