why does probplot return negative/larger than 1 values ?
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is supposed to show the probability distrbution of the values in Y. so probability cant be negative or larger than 1 but if i check
it has both negative values and values larger than 1. how is that possible ? perhaps i misunderstood something?
Walter Roberson on 9 Oct 2015
get(h,'ydata') is going to return whatever data the routine needed to generate in order to plot nicely. If you look at the y axis locations you can see that the spacing is not nearly equidistant in probability value, with values being close together near the middle and further apart near the top or bottom.
A plausible explanation would be that the data stored is in terms of standard deviations from mean 0.5
Image Analyst on 10 Oct 2015
In the Statistics and Machine Learning Toolbox:
[f,xi] = ksdensity(x,pts) returns a probability density estimate, f, for the sample in the vector x, evaluated at the specified values in vector pts. Here, the xi and pts vectors contain identical values.
[pdca,gn,gl] = fitdist(x,distname,'By',groupvar) creates probability distribution objects by fitting the distribution specified by distname to the data in x based on the grouping variable groupvar. It returns a cell array of fitted probability distribution objects, pdca, a cell array of group labels, gn, and a cell array of grouping variable levels, gl.