Collection of Data

Collection of Data

Primary data are first-hand original data that we collect ourselves. Primary data collection can be done in a variety of ways such as by conducting personal interviews (by phone, mail or face-to-face), by conducting experiments, etc.,

Secondary data are the data taken from figures  collected by someone else. For example, government-published statistics, available research reports etc.,

Progress Check

Identify the primary data

(i) Customer surveys

(ii) Medical researches

(iii) Economic predictions

(iv) School results

(v) Political polls

(vi) Marketing details

(vii) Sales forecasts

(viii) Price index details

1. Getting the Facts Sorted Out

When data are initially collected and before it is edited and not processed for use, they are known as Raw data. It will not be of much use because it would be too much for the human eye to analyse.

For example, study the marks obtained by 50 students in mathematics in an examination, given below:

Activity − 1

Prepare an album of pictures, tables, numeric details etc that exhibit data. Discuss how they are related to daily life situations.

61 60 44 49 31 60 79 62 39 51 67 65 43 54 51 42

52 43 46 40 60 63 72 46 34 55 76 55 30 67 44 57

62 50 65 58 25 35 54 59 43 46 58 58 56 59 59 45

42 44

In this data, if you want to locate the five highest marks, is it going to be easy? You have to search for them; in case you want the third rank among them, it is further  complicated. If you need how many scored less than, say 56, the task will be quite time consuming.

Hence arrangement of an array of marks will make the job simpler.

With some difficulty you may note in the list that 79 is the highest mark and 25 is the least. Using these you can subdivide the data into convenient classes and place each mark into the appropriate class. Observe how one can do it.

From this table can you answer the questions raised above? To answer the question, “how many scored below 56”, you do not need the actual marks.

You just want “how many” were there. To answer such cases, which often occur in a study, we can modify the table slightly and just note down how many items are there in each class. We then may have a slightly simpler and more useful arrangement, as given in the table.

This table gives us the number of items in each class; each such number tells you how many times the required item occurs in the class and is called the frequency in that class.

The table itself is called a frequency table.

We use what are known as tally marks to compute thefrequencies. (Under the column ‘number of items’, we do not write the actual marks but just tally marks). For example, against the class 31-35, instead of writing the actual marks 31, 34, 35 we simply put |||. You may wonder if for the class 56-60 in the example one has to write ||||||||||| , making it difficult to count. To avoid confusion, every fifth tally mark is put across the four preceding it, like this  . For example, 11 can be written as  . The frequency table for the above illustration will be seen as follows:

 Note

Consider any class, say 56- 60; then 56 is called the lower limit and 60 is called the upper limit of the class.

Progress Check

Form a frequency table for the following data:

23 44 12 11 45 55 79 20

52 37 77 97 82 56 28 71

62 58 69 24 12 99 55 78

21 39 80 65 54 44 59 65

17 28 65 35 55 68 84 97

80 46 30 49 50 61 59 33

11 57