Organisation of Data | Class 11 Economics Notes

How to Prepare a Frequency Distribution?

This section details the practical steps and considerations in preparing a frequency distribution. Five key questions guide the process: (1) Should class intervals be equal or unequal? (2) How many classes should be formed? (3) What should be the size of each class? (4) How to determine class limits? (5) How to find the frequency for each class? Equal class intervals are generally preferred unless data range is very large or data are concentrated in specific ranges, in which case unequal intervals are better. The number of classes is usually between six and fifteen, determined by dividing the range (difference between largest and smallest values) by class interval size. Class limits should be definite and clear; open-ended classes like '70 and over' are discouraged. Two types of class intervals are explained: inclusive (both limits included) and exclusive (one limit excluded). For discrete variables, both methods are used; for continuous variables, inclusive intervals are common. Examples illustrate inclusive and exclusive intervals for marks ranging 0–100. For continuous variables like height or weight, class intervals are expressed as '30 Kg and above but less than 40 Kg' to maintain continuity. Table 3.4 shows income distribution with gaps between classes; this is corrected by adjusting class limits by 0.5 units to restore continuity (Table 3.5). Frequency is obtained by tally marking raw data against classes, facilitating easy counting. The section emphasizes clarity and consistency in class formation to ensure meaningful analysis.

📊 Diagram: See table_7: Table on page 10 (8×2); See table_8: Table on page 11 (8×2)

🧪 Activity: Find the range of the population of India in Example 1 and the yield of wheat in Example 2.

🔗 Connection: Prepares for the next section on Frequency Distribution with Unequal Classes, addressing special cases.

Table on page 10 (8×2)

Table on page 11 (8×2)