(i) Variable: Any character that can vary from one individual to another is called variable or variable
(ii) Class interval: In the data each group into which raw data is considered is called a class-interval.
(iii) Class-size: The different between the true upper limit and lower limit is called the class size of that class.
(iv) Class mark: The middle value of the class is called as the class mark.
Class mark = (Upper Limit + Lower Limit)/2
(v) Frequency: The number of observations corresponding to class is called its frequency.
(vi) Class limits: Each class is bounded by two figures, called the class limits. The figures on the left side of the classes are called lower limits while figures on the right side are called upper limits.
(vii) True class limits: if classes are inclusive eg 15-19, 20-24, 25-29, 30-34..........
Then, true lower limit of class = upper limit of class -0.5
And true upper limit of class = upper limit of class +0.5
Example: true limits of the class 15-19 are 14.5 and 19.5
But if because classes are exclusive use like 10-20, 20-30, 30-40........
Here class limits and true class limits are the same.
