Frequency Table for Interval Data

Data may be discrete or continuous. Discrete data can only take particular values (usually whole numbers) such as the number of children per family. Continuous data can take any value in a given range, for example mass, height, age and temperature.

Sometimes, the collected data can be too numerous to be meaningful. We need to organise data in some logical manner in order to make sense out of them. We could group data into classes. Each class is known as a class interval.

Example :

The data below shows the mass of 40 students in a class. The measurement is to the nearest kg.

55	70	57	73	55	59	64	72
60	48	58	54	69	51	63	78
75	64	65	57	71	78	76	62
49	66	62	76	61	63	63	76
52	76	71	61	53	56	67	71

Construct a frequency table for the data using an appropriate scale.

Solution:

Step 1:Find the range.

The range of a set of numbers is the difference between the least number and the greatest number in the set

In this example, the greatest mass is 78 and the smallest mass is 48. The range of the masses is then 78 – 48 = 30. The scale of the frequency table must contain the range of masses. .

Step2: Find the intervals

The intervals separate the scale into equal parts.

We could choose intervals of 5. We then begin the scale with 45 and end with 79

Step 3: Draw the frequency table using the selected scale and intervals.

Mass (kg)	Frequency
45 – 49	2
50 – 54	4
55 – 59	7
60 – 64	10
65 – 69	4
70 – 74	6
75 – 79	7

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