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An Introduction to the NAG Statistical Add-Ins for Excel - Basic Statistics

The first stage of many analyses is to explore the data, producing useful descriptive statistics. The NAG Statistical Add-Ins  give you a range of functions to make this process easy in Excel. The example below illustrates how to produce a basic 5 point summary of some data. The data used refers to various details of cars for sale in 1997.

At any time you can view the screenshots at full size by clicking on the image.

The first thing to do is to place the cursor in an empty cell, where we wish the output of the function to be displayed. For this example we created a new worksheet for the results and placed the cursor in cell A1. Next we select the required NAG function. As we wish to produce a 5 point summary of our data, after clicking on the function wizard button (highlighted in red), we either select the All or Statistical function category and then scroll down to select the S5PT_SUMMARY function from the Function name: list.

Figure 1: Selecting the function (click image to view)

Once we have selected the required function, the specific function wizard will appear. We must now tell Excel which data we wish to be summarised. In this example, we wish to obtain the 5 point summary for the prices of the different cars in our sample so, after placing the cursor in the X fieldbox of the function wizard, select cell B2 in data worksheet. While holding the left mouse button down, highlight cells B2 to B34.

Once we have done this, the selected data will be displayed in the X fieldbox (highlighted red), whilst details of the expected output will also be displayed (highlighted blue) - in this case, that a list ranging over 11 cells should be expected.

Figure 2: Selecting the data (click image to view)

Returning to our results worksheet, the <List of 11> message will appear in cell A1, indicating that the calculations have been successfully completed. Now all we need to do is to extract the results themselves.

Figure 3: Successful completion of calculations (click image to view)

To obtain the results of an Excel function, follow the following steps:

1. Place the cursor in the original output cell.
2. Holding down the left mouse button, drag the cursor down until the number of cells stated in the <list of ...> message have been highlighted. In this case we have to highlight 11 cells in order to display all the function output.
3. Place the cursor in the Formula Bar and, whilst holding down the Ctrl and Shift keys, press the Enter key.

Figure 4: Displaying the results (click image to view)

The function output will now be displayed in cells A1 to A11 of our output worksheet and we can see that the prices of the cars in our sample range from £5,245 to £95,510.

Figure 5: the 5 point summary of car price data (click image to view)

All of the NAG Statistical Add-Ins for Excel operate in the same manner; select the function, provide appropriate parameters for the function wizard fieldboxes, highlight the required number of output cells and then press Ctrl+Shift+Enter to display the output. By following these steps, many simple and complex statistical analyses alike can readily be performed, helping you make the most of your data in an environment you are comfortable with.