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September 1st, 2018, 06:04 PM   #1
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Statistics using Excel

I have been working on a project and it's been several years since I've taken statistics and I've never really used excel for this sort of stuff so I am uncertain if my process is correct. I'm hoping someone will be able to provide some guidance.

I am working on something with tornado data and I am looking to determine if a certain period (could be a month, year, or season) is above-average or below-average, and if so, how much above or below. To do this I was going to create standard deviations.

In Excel, I have tornado data for all March's from 1950-1965. I used the average function to give me an average and then I used the STDEV.P function to yield some standardized number. (I'm hoping the STDEV.P function was the correct choice to choose).

Anyways...so the average doesn't get skewed by any major outliers I want to see if there are any outliers so they don't get used to find the average and standardized number. So this is what I was doing.

Using the QUARTILE.INC function I found the value for Q1 and then Q3. From here I did Q3 - Q1 to get the IQR. I multiplied the IQR by 1.5. To find the lower quartile I did Q1 - ((1.5)(IQR)) and to find the upper quartile I did Q3 + ((1.5)(IQR))

What I think I am confused with is don't you need to find the median or something and the data has to be in sequential order?

As for getting the standard deviation what I did was take a value, subtracted it from the average, and then divided by the standardized number. For example...

The March 1950-1965 average is 40.38 and the standardized number is 25.0471. March of 1966 had 12 tornadoes...so 12 -40.38 = -28.38 -----> divided by 25.0471 = -1.13 so compared to the 1950-1965 average, March of 1966 was -1.13 standard deviations below average.

Is this process/method correct?
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