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bkeagles
11-18-2005, 09:52 PM
Can anyone explain normal distribution?

Is the following normally distributed and if so why, if no then why not? Is is close?

NN Valid 25
Missing 25

Mean 28.5200
Std. Error of Mean 3.37250
Median 25.0000
Std. Deviation 16.86248

I would appreciate any help anyone can offer.

Thanks Mary

quark
11-18-2005, 10:02 PM
Mary,

You cannot tell if it's normal distribution if you only know the mean, sd etc. You can first try plotting data to see if the graph is bell shaped. If it is, do a normal probability plot to assess if the data is normally distributed.

JohnM
11-18-2005, 10:04 PM
Mary,

It's really impossible to tell if a data set is normally distributed unless you can take a look at the individual data points in a histogram or normal probability plot.

In your case, all you have are summary statistics - with that you can get a rough idea about the symmetry of the distribution (i.e., if the mean and median are really close), but not much more than that.

John

bkeagles
11-19-2005, 06:24 PM
. I am not sure what the graphs are telling me. Is it a normal distribution? Why or Why not?

I tried to attach the graphs to this e-mail. If you can see them please give me some feedback.

The graph is on the last page of the attached document.

JohnM
11-19-2005, 09:00 PM
I would say that this is not normally distributed, because the histogram (the bars) do not "fit" the normal curve that overlays the bars. You don't need a "perfect" fit, but it should be close.

quark
11-19-2005, 10:12 PM
I agree with John. The histogram is not symmetric around the mean, and there are many outliers at 70-80. It's too skewed to be normally distributed.