Calculate Average Temperature Data

How do you think the overall monthly temperature averages for your selected area compare to the average temperatures during the 1997-98 El Niņo event?

If you tried to visually analyze all the data in your spreadsheet at once, interpretation would be too difficult. One way to handle this problem is to calculate monthly averages for the entire set of data. First create a new "Average" row under the last row of data. Then for each month, in the new Average row you created, calculate the average as follows: Type "=AVERAGE( )" with the cell range reference inside the parentheses; for example, =AVERAGE(B4:B89)

As you look down the rows of data for each month, you can see that the temperature varies from year to year. Comparing data from El Niņo years to "average" temperatures would not reflect that variability. Instead, we need a way compare the data to what are the normal, or typical, temperature ranges. 

Calculating the standard deviation allows you to take into account these ranges in temperature each month, assuming the data are normally distributed, as is often the case with temperature data. You can use the standard deviation function of the spreadsheet to express the variability of the average monthly temperatures you determined earlier. 

Create three more rows under the Average row: one to calculate the Standard Deviation [=STDEV(insert cell range)] for each column, one for Average +1 standard deviation (add the Average and the Standard Deviation cells for each column), and a third row to calculate the average -1 standard deviation (subtract the Standard Deviation cell from the Average cell for each column). 

By definition, approximately 68% of the data from the temperature table will fall between +1 and -1 standard deviation of the average. You can use this range as an indication of typical temperatures for the month.

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