# z-score for two variables

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?

## 1 Answer

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