# [R] qqplot for binomial distribution

Ashim Kapoor ashimkapoor at gmail.com
Tue Apr 18 06:47:01 CEST 2017

Dear Boris,

> dput(count1_vector)
c(5, 6, 4, 4, 6, 5, 4, 5, 3, 7, 5, 5, 3, 4, 8, 6, 10, 2, 4, 6,
8, 4, 4, 6, 8, 5, 6, 3, 7, 9, 4, 7, 5, 7, 3, 4, 5, 2, 11, 7,
8, 5, 5, 6, 3, 2, 3, 5, 9, 6, 5, 6, 7, 3, 10, 7, 6, 4, 9, 5,
7, 3, 7, 3, 2, 3, 4, 5, 10, 4, 5, 5, 6, 7, 4, 8, 7, 5, 5, 4,
8, 7, 9, 4, 4, 4, 7, 5, 4, 10, 4, 5, 6, 1, 3, 5, 4, 7, 4, 6)

set.seed(123)
qqplot(count1_vector,rbinom(n=100,size=100,p=.05))
qqline(count1_vector,distribution = function(probs) { qbinom(probs,
size=100, prob=0.05) },
col = "red",
lwd = 0.5)

When I do this, the line does not pass through the center of my data.I do
expect count1_vector to be 100 samples of binomial with n=100 and p=.05.

Any comments or suggestions for me ?

Note : I built a 95% Confidence interval for my data and I counted how
often out of 100 times did the data fall outside the CI.This I expect to be
binomial with n=100,p=.05. I repeated this a 100 times and obtained
count1_vector.

Best Regards,
Ashim.

On Mon, Apr 17, 2017 at 7:51 PM, Boris Steipe <boris.steipe at utoronto.ca>
wrote:

> That's not how qqline() works. The line is drawn with respect to a
> _reference_distribution_ which is the normal distribution by default. For
> the binomial distribution, you need to specify the distribution argument.
> There is an example in the help page that shows you how this is done for
> qchisq(). for qbinom() it is:
>
>
> set.seed(123)
> qqplot(rbinom(n=100, size=100, p=0.05),
>        rbinom(n=100, size=100, p=0.05) )
>
> qqline(rbinom(n=100,size=100,p=.05),
>        distribution = function(probs) { qbinom(probs, size=100, prob=0.05)
> },
>        col = "red",
>        lwd = 0.5)
>
>
>
>
> B.
>
>
> > On Apr 17, 2017, at 9:15 AM, Ashim Kapoor <ashimkapoor at gmail.com> wrote:
> >
> > Dear Spencer,
> >
> > Okay. Many thanks. My next query is how do I use qqline?
> >
> > When I try
> >
> >> qqline(rbinom(n=100,size=100,p=.05))
> >
> > I don't get the line in the right place.
> >
> > Best Regards,
> > Ashim
> >
> > On Mon, Apr 17, 2017 at 6:31 PM, Spencer Graves <
> > spencer.graves at effectivedefense.org> wrote:
> >
> >>
> >>
> >> On 2017-04-17 7:58 AM, Ashim Kapoor wrote:
> >>
> >>> Dear All,
> >>>
> >>> set.seed(123)
> >>> qqplot(rbinom(n=100,size=100,p=.05), rbinom(n=100,size=100,p=.05) )
> >>>
> >>> I expect to see 1 clear line,but I don't. What am I misunderstanding?
> >>>
> >>
> >>
> >>      The distribution is discrete, and points are superimposed. Try the
> >> following:
> >>
> >>
> >> set.seed(123)
> >> qqplot(jitter(rbinom(n=100,size=100,p=.05)),
> >>       jitter(rbinom(n=100,size=100,p=.05) ))
> >>
> >>
> >>      Spencer Graves
> >>
> >>>
> >>> Best Regards,
> >>> Ashim
> >>>
> >>>        [[alternative HTML version deleted]]
> >>>
> >>> ______________________________________________
> >>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >>> https://stat.ethz.ch/mailman/listinfo/r-help
> >>> ng-guide.html
> >>> and provide commented, minimal, self-contained, reproducible code.
> >>>
> >>
> >> ______________________________________________
> >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> ng-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help