Plotting F Distribution Probability Distribution Function

**diggetybo** · 02-23-2015, 12:09 PM

Hello,

I'm trying to plot a F PDF as seen at the bottom of this link: http://www.mathworks.com/help/stats/f-distribution.html

I'm using excel 2007.
X Axis: I have a column for the positive real number domain including zero, in increments of .01, looks something like this...
A1:X
A2:0
A3:0.01
.
.
.
A1001:10

Y Axis: I tried using the formula =FDIST(A2,5,3) to compute the y axis values, but my values are very different than the mathworks' site.

B1:Y
B2:1
B3:0.99993
.
.
.
B1001: 0.043419

Just from plotting the graph, I can tell that something is not right, the shape is not the same as the example, and the mathwork's graph doesn't have any y axis values over .6.

Why does the excel f distribution PDF look different? Why does it have a .999?

Please advise on what approach I should take to reproduce the results on the mathworks site.

Thanks!

**shg** · 02-23-2015, 01:23 PM

The F.DIST function is new to Excel 2010 and generates the distribution you're looking for (the left-tailed distribution); it is not available in Excel 2007. There's probably a way to calculate it using the available functions, but I don't know how. Some stats person here probably does.

The Excel 2007 FDIST function is superseded by F.DIST.RT, which generates the result you're seeing. You would think they would have named the new functions F.DIST.LT and FDIST.RT (for Left and Right) to avoid confusion.

**diggetybo** · 02-23-2015, 01:36 PM

Oh I see. Thank you very much shg. That would explain why. Windows 2007... can't believe it's been over seven years.

Hmm, personally, I'm going to wait until Windows 10 comes out then get everything together.

Meanwhile, could someone help with manually plotting that kind of F distribution?

Thanks again!

I will post the graph here for easy reference.

F Distribution.png