NCERT Book Class 11 Statistics Collection of Data

Collection of Data

chapter, you will study the sources of data and the mode of data collection. The purpose of collection of data is to collect evidence for reaching a sound and clear solution to a problem.In economics, you often come across a statement like, “After many fluctuations the output of food grains rose to 176 million tonnes in 1990–91 and 199 million tonnes in 1996–97, but fell to 194 million tonnes in 1997–98. Production of food grains then rose continuously and touched 212 million tonnes in 2001–02.” In this statement, you can observe that the food grains production in different years does not remain the same. It varies from year to year and from crop to crop. As these values C H A P T E R 2vary, they are called variable. The variables are generally represented by the letters X, Y or Z. The values of these variables are the observation. For example, suppose the food grain production in India varies between 100 million tonnes in 1970–71 to 220 million tonnes in 2001–02 as shown in the following table. The years are represented by variable X and the production of food grain in India (in million tonnes) is represented by variable Y:

2. WHAT ARE THE SOURCES OF DATA?

Statistical data can be obtained from two sources. The enumerator (person who collects the data) may collect the data by conducting an enquiry or an investigation. Such data are called Primary Data, as they are based on first hand information. Suppose, you want to know about the popularity ofa film star among school students. For this, you will have to enquire from a large number of school students, by asking questions from them to collectthe desired information. The data you get, is an example of primary data. If the data have been collected and processed (scrutinised and tabulated)by some other agency, they are called Secondary Data. Generally, the  published data are secondary data.They can be obtained either frompublished sources or from any othersource, for example, a web site. Thus, the data are primary to the source that collects and processes them for the first time and secondary for all sources that later use such data. Use of secondary data saves time and cost. For example, after collecting the data on the popularity of the film star among students, you publish a report. If somebody uses the data collected by you for a similar study, it becomessecondary data.

EXERCISES

1. Frame at least four appropriate multiple-choice options for following questions:

(i) Which of the following is the most important when you buy a new dress?

(ii) How often do you use computers?

(iii) Which of the newspapers do you read regularly?

(iv) Rise in the price of petrol is justified.

(v) What is the monthly income of your family?

2. Frame five two-way questions (with ‘Yes’ or ‘No’).

3. (i) There are many sources of data (true/false).

   (ii) Telephone survey is the most suitable method of collecting data, when the population is literate and spread over a large area (true/false).

   (iii) Data collected by investigator is called the secondary data (true/false).

   (iv) There is a certain bias involved in the non-random selection of samples (true/false).

   (v) Non-sampling errors can be minimised by taking large samples (true/ false).

4. What do you think about the following questions. Do you find any problem with these questions? If yes, how?

   (i) How far do you live from the closest market?

   (ii) If plastic bags are only 5 percent of our garbage, should it be banned?

   (iii) Wouldn’t you be opposed to increase in price of petrol?

   (iv) (a) Do you agree with the use of chemical fertilizers?

(b) Do you use fertilizers in your fields?

(c) What is the yield per hectare in your field?

5. You want to research on the popularity of Vegetable Atta Noodles among children. Design a suitable questionnaire for collecting this information.

6. In a village of 200 farms, a study was conducted to find the cropping pattern. Out of the 50 farms surveyed, 50% grew only wheat. Identify the population and the sample here.

7. Give two examples each of sample, population and variable.

8. Which of the following methods give better results and why?

  (a) Census (b) Sample

9. Which of the following errors is more serious and why?

  (a) Sampling error (b) Non-Sampling error

10. Suppose there are 10 students in your class. You want to select three out  of them. How many samples are possible?

11. Discuss how you would use the lottery method to select 3 students out of 10 in your class?

12. Does the lottery method always give you a random sample? Explain.

13. Explain the procedure of selecting a random sample of 3 students out of 10 in your class, by using random number tables.

14. Do samples provide better results than surveys? Give reasons for your answer.

Please refer to attached file for NCERT Class 11 Statistics Collection of Data