Re: Histogram chart - What do the y-axis numbers mean?

[Jean Bréfort <jean brefort normalesup org>]

Le vendredi 12 septembre 2008 à 15:28 -0400, Marlon Nelson a écrit :
> Thank you, Jean
>
> Another question:  The data table was produced using the Histogram
> tool.  The 1% bin counts 1011 data points between -1% and 1%.  In the
> chart of the histogram, the area representing those points falls
> between 1% and 3% on the x-axis.  Seems like an off-by-one problem to
> me.

The histogram plot needs one more x data than y data the first y data is
assumed to represent the number of occurences between the two first x
data. I have plans to implement hidtograms from raw data at some moment
in the future.

Regards,
Jean

> On Fri, Sep 12, 2008 at 11:17 AM, Jean Bréfort <jean brefort free fr> wrote:
> > Le vendredi 12 septembre 2008 à 10:46 -0400, Marlon Nelson a écrit :
> > > I originally thought this was a bug and was about 30 seconds from
> > > submitting one to bugzilla when I began to suspect the problem is with
> > > my understanding of what a histogram is.
> > >
> > > With the data listed below (frequency of daily returns of Merrill
> > > Lynch stock over the last 10 years), I created a histogram chart.  The
> > > highest point on the chart reaches 50,000.  I was expecting 1011.
> > >
> > > Reading a bit from wikipedia, I see what I was actually expecting to
> > > see is a bar chart.
> > >
> > > But given a histogram chart of this data, what do the y-axis numbers mean?
> > >
> > > Bin   Frequency
> > > -15%  1
> > > -13%  1
> > > -11%  4
> > > -9%   6
> > > -7%   13
> > > -5%   53
> > > -3%   167
> > > -1%   510
> > > 1%    1011
> > > 3%    489
> > > 5%    156
> > > 7%    57
> > > 9%    26
> > > 11%   6
> > > 13%   4
> > > 15%   3
> > > 17%   2
> > >
> > > --
> > > -eom-
> >
> > The histogram plots the density, as the 1011 data are in a 0.02
> > interval, you get 1011 / 0.02 = 50550 as the largest value.
> >
> > Regards,
> > Jean