Ways of checking statistics questions

If you have time to review your work in the exam always try to check using a different approach than the one you used to do the question in the first place.

Quick reasonableness checks on the mean and standard deviation would be:

• Is the mean roughly in the middle of my data?
• Does the interval from mean-sd to mean+sd include about two thirds of my data?

Another way to check questions about mean and standard deviation is to choose a coding, one which makes the numbers as simple as possible, so that you can do most of the calculations without a calculator.

Coding works well with exam questions, where the numbers are contrived, it is less relevant in the real world where the numbers tend to be messier, but in the real world you use a computer to crunch the numbers so it doesn't matter.

Note that in the real world it is still very important to use common sense reasonableness checks if you can, like checking that the mean and standard deviation are what you would expect.

When choosing your coding look to subtract a number near the mean or mode. Choosing the mode is good because it means you will have several 0's in your coded data. Also divide by something simple (2, 10, 100) if it makes things easier, but only choose something you can do in your head.

When you have chosen your coding, write it down clearly. If you don't, you are guaranteed to make mistakes.