GRAPHING A BINOMIAL PROBABILITY DISTRIBUTION USING …



GENERATING AND GRAPHING A BINOMIAL PROBABILITY DISTRIBUTION USING EXCEL

Suppose you wish to generate the probability distribution for a binomial random variable for which there are 5 trials (n = 5) and the probability of success is .3 (p = .3). Do the following:

1. Input the possible values for X in the spreadsheet:

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2. Move to the cell next to X = 0 (cell B2 in this example) and type "=" then click "fx" above the spreadsheet.

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3. In the "Or select a category" section of the dialog box, choose "Statistical" then choose "BINOMDIST" in the "Select a function:" section of the dialog box and click "OK." The following will appear:

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4. Fill in the dialog box appropriately, i.e., I'll set "Number_s" to "a2" since X=0 is in cell a2, Trials are "5" in this example, and the Probability_s is .3 per the information given above. I type in the word "false" in the Cumulative box (since if I typed in "true" Excel would give the cumulative distribution function rather than the probability distribution function). Click "OK" when finished.

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5. Excel returns the P(X=0). Place your cursor on the lower right hand corner of cell B2 and do a "drag and fill" for the rest of the probabilities.

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Now to graph the probability distribution do the following:

1. Click on the chart wizard

2. Click on the column chart option, then click next

3. For data range, mark the cells of the P(X=x) column and remain in this dialog box

4. Now click the "Series" tab

5. Go to the "Category X Axis Labels" box and put in the cell range for the X column of the spreadsheet (but don't include X itself). Then click next

6. Edit chart title, X axis title, and Y axis title to taste and click next.

7. Click finish

Having correctly followed these steps, you should get a graph that looks like this--

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