An important practice is to check the validity of any data set that you analyze.

Question

An important practice is to check the validity of any data set that you analyze. One goal is to detect typos in the data, and another would be to detect faulty measurements. Recall that outliers are observations with values outside the “normal” range of values of the rest of the observations.

Specify a large population that you might want to study and describe the type numeric measurement that you will collect (examples: a count of things, the height of people, a score on a survey, the weight of something). What would you do if you found a couple outliers in a sample of size 100? What would you do if you found two values that were twice as big as the next highest value?

You may use examples from your area of interest, such as monthly sales levels of a product, file transfer times to different computer on a network, characteristics of people (height, time to run the 100 meter dash, statistics grades, etc.), trading volume on a stock exchange, or other such things. It is not required that the example is from your area of interest, that is just a suggestion.

Explanation / Answer

Area of interest : Marks obtained by students in Maths Exam

Let us consider a maths exam conducted by a university for all its students. The maximum marks which can be obtained by a student is 100

Now in our sample of 100 students if we find a couple of outliers we first check whether this has occurred due to a typo or has the student really secured such high marks

This can be cross checked by totalling the marks obtained by the student in the exam

The other method is that we can use a z score to calculate how far from the expected standard deviation is the score

If the z sore is very high ie more than 3 standard deviations away from the mean we can safely assume that there has been a error while entering the data

If the values were twice as big as the next highest value we first check if the value is more than 100

I fit is more than 100 we can say that there has been a typo in entering the marks of the students

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