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Can we study the relationship between two variables using z score? For example: Let us say that we have two classes A, B and we have 5 students in each class and we know the age and the grade for every student. and we want to study the relationship between age and the grades. 

  age     class A  grades             
  10       75
  13       85
  20       55
  16       45
  19       90

  age     class B  grades
  12       65
   9       54
  13       67
  21       90
  23       85

If we calculate the Z score for age and for the grades then we can estimate how far is the grades or the ages from the mean. How can we visualize the relationship between the grades and the age using Z score in this case?

goro
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    You might want to explore some of our higher-rated threads on [correlation](http://stats.stackexchange.com/search?tab=votes&q=correlation%20standardize%20z-score). I believe the question at http://stats.stackexchange.com/questions/70969 may be practically the same. – whuber Oct 29 '14 at 20:51

1 Answers1

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You can calculate the z score for individual data points within either data set. You could then compare these z scores for a gauge on the differences between the data points. Since the z score is calculated for each individual data point, however, it is not generally a useful tool for comparing one data set with another data set. It is better suited to comparing data points to each other. I recommend the following videos to better understand z score.

http://www.snappyeducation.com/#!z-score/c1msv

user62190
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