Some Basic Definitions.docx

SOME BASIC DEFINITIONS (i) Variate: Variate is a quantity that may vary from observation to observation. (ii) Range: Range is difference between the maximum and minimum observations. (iii) Class Interval: When data are divided in groups, each group is called a class interval. (iv) Class Limit: Every class interval has two limits. The smallest observation of the interval is called lower limit and the largest observation of the interval is called upper limit. (v) Class Mark: The mid value of any class is called its class mark. Class Mark = Upper limit of the class + lower limit of the class 2 (vi) Class Size: Class size is defined as the difference between two successive class marks. It is also the difference between the upper and lower limits of any class interval. (vii)

Frequency: In a particular class the count of the number of observation is

called its frequency. So the corresponding frequency of a class is called its class frequency. (viii)

Cumulative Frequency: The cumulative frequency of any class is obtained

by adding all the frequencies successively prior to that class i.e. it is the sum of all frequencies up to that class. Inclusive and Exclusive distributions: Inclusive Distribution : When in a distribution, the upper limit does not coincide with the lower limit of the next class then the distribution is called an inclusive distribution. e.g. Inclusive Form Height (in cm)

No. of Students

150-152

4

153-156

10

157-169

6

170-173

3

Exclusive Distribution: An exclusive distribution is that distribution in which the upper limit of one class coincides with the lower limit of the next class. e.g. Inclusive Form Height (in years)

No. of Students

10-20

10

20-30

8

30-40

15

40-50

4

True Class Limit: In the case of exclusive classes the upper and lower limits are respectively known as its true upper limits and true lower limits. In the case of inclusive classes, the true lower and upper limits are obtained by subtracting 0.5 from the lower limit and adding 0.5 to the upper limit. True upper limits and true lower limits are also known as boundaries of the class. Tally: Tally method is used to keep the chance of error at minimum in counting. A bar (|) called tally mark is put against any item when it occurs. The fifth occurrence of any item is represented by putting diagonally a cross tally (|) on the first four tallies.