All,

    Thanks for all of your help & advice!  I created a plot starting with
qqnorm, if I remember right, but I had to add a LOT of extras.  I was
surprised that it doesn't include the probability (e.g. 50% at mean) and
instead provides the standard deviations (e.g., 0 at mean) on the axis.
Plus, there is no line through Q1 & Q3 to help give a sense of the normality
of the graph.
    I added these things & was in the end happy with the code, but it was
surprisingly not trivial.  The qqnorm & qqplot, as given, are not too useful
for any practical engineering analysis.  I am not yet savvy enough with 'R'
to create a package, but if anyone out there is curious, let me know & I can
supply the code.

                                      Thanks!
                                            Mike


On Thu, Dec 18, 2008 at 4:21 AM, Mike Lawrence <mike@thatmike.com> wrote:

> On Mon, Dec 15, 2008 at 9:48 PM, Mike Williamson <this.is.mvw@gmail.com>wrote:
>
>>    I want to make some simple CDF (cumulative distribution function) plots
>> to check whether distributions are Gaussian / normal.
>
>
> qqnorm()
>
>
>>    As long as I am asking:  I also want to plot more than one distribution
>> or group.  For instance, I want to plot 3 different factors on the same
>> graph, where each factor has it's own cdf line.  Any ideas for this?
>
>
> a=qqnorm(rnorm(100))
> b=qqnorm(runif(100))
>
> plot(
> a$x[order(a$x)]
>  ,a$y[order(a$x)]
> ,type='l'
> ,ylim=c(min(c(a$y,b$y)),max(c(a$y,b$y)))
>  ,xlim=c(min(c(a$x,b$x)),max(c(a$x,b$x)))
> )
> lines(
> b$x[order(b$x)]
>  ,b$y[order(b$x)]
> ,col='red'
> )
>
> --
> Mike Lawrence
> Graduate Student
> Department of Psychology
> Dalhousie University
> www.thatmike.com
>
> Looking to arrange a meeting? Do so at:
> http://www.timetomeet.info/with/mike/
>
> ~ Certainty is folly... I think. ~
>



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