Organisation and Classification of Data

Organisation and Classification of Data

After collecting data it has to be classified and arranged for further statistical analysis. The data classified is large in quantity needs to be reduced for further analysis. This leads to organization of data.

Following steps are important in organization of data

Finding Range

While organizing the data, it is necessary to find out the highest and lowest number (maximum and minimum value) from the given data. The difference between these two extreme values is called range.

Range = Highest value − Lowest value.

Example

Find out the range from the following data 2, 6, 4, 9, 12, 8, 5, 8. In this case, highest value is 12 and lowest value is 2, and the range is 12 – 2 = 10.

Frequency array

In statistics, array refers to some kind of orderly arrangement. When the numerical raw data is arranged in ascending or descending order, it is called array.

Frequency distribution

It is an arrangement of data into classes. Following technical terms are important for frequency distribution.

1. Class

It is a group which divides the variable into parts and forms a set of given frequency.

Example

2. Class limit

The extreme values of the classes or groups are called the class limit. Each class has lower limit (minimum value) and upper limit (maximum value).

For example in the class 10 − 20, the lower limit is 10 and upper limit is 20.

3. Midpoint

It is obtained by dividing the sum of lower limit and upper limit by 2.

For example in the class 10 – 20, the Midpoint10+20/2=15

4. Class interval

It is the difference between the upper and lower limit of a class.

For example:

In the class 10 – 20,

The class interval is 20 − 10 = 10

5. Tally Marks

Tally marks usually come in group of 5. For every observation, we put vertical bars called tally marks. After 4 bars we put a cross stroke for 5th observation. It helps in easy counting of the frequencies.

6. Class Frequency

The number of observations included in each class is the class frequency or sum of tally marks of that particular class.

7. Total Frequency

It is an aggregate of all class frequencies. It is the sum of all observations.