P

#### P.-S. ROSS

using any plug-ins. I want a normal probability curve

(having the same mean and standard deviation than my raw

data) superimposed on the histogram, like normal

statistical software do automatically.

First I compute the absolute frequencies of the classes

(from the raw data) using the FREQUENCY function. The

relative frequencies are calculated by dividing the

absolute frequencies by the number of data (n). A bar

chart of the relative frequency vs. class middle point

yields the histogram. I know there is a "histogram"

function in the analysis tool that does that, but

nevermind, this is not my problem.

So now I need a normal probability curve. First I

calculate the mean and st. dev. of my raw data using the

appropriate functions (AVERAGE, STDEV). Then I use the

function NORMDIST(x,mean,standard_dev,cumulative), where x

is an arbitrary value for which I want the normal

probability, and "cumulative" is a logical operator set

to "FALSE" to return the probability mass function rather

than the cumulative function. I use enough x values in the

relevant range to get a smooth probability curve, and this

makes a nice graph, with an horizontal axis directly

comparable to that of the histogram. The vertical axis of

this second graph, however, is not directly comparable to

that of the histogram. So my problem is how to adjust the

results of the function NORMDIST so that the values are

directly comparable to the relative frequencies in my

histogram.

And, idealy, how to merge the histogram and the normal

probability curve in a single diagram, using only MS Excel

(Office 2000 version).