Class | Subject | Book | Chapter | Session | Questions covered |
|---|---|---|---|---|---|
XI | Economics | Statistics for Economics (NCERT) | 2 – Collection of Data | 2026-27 | 14 of 14 |
Chapter at a glance
Topic | Key facts |
|---|---|
Sources | Primary data (collected first-hand by the investigator) and secondary data (already collected by others) |
Instruments | Questionnaire or interview schedule: short, simple, logical order, no leading or ambiguous questions |
Survey modes | Personal interview, mail survey, telephone interview; pilot survey first |
Census vs sample | Census covers every unit of the population; a sample is a representative part |
Sampling | Random (lottery, random number tables) and non-random (judgement, quota, convenience) |
Errors | Sampling error (sample vs population value), non-sampling error (measurement, non-response, sampling bias) |
Agencies | Census of India, NSO (formerly NSSO), RGI, DGCIS, Labour Bureau |
Exercise Questions
Frame at least four appropriate multiple-choice options for following questions:
Answer
- Which of the following is the most important when you buy a new dress?
- How often do you use computers?
- Which of the newspapers do you read regularly?
- Rise in the price of petrol is justified.
- What is the monthly income of your family?
Answer
(i) Most important when buying a new dress: (a) Price (b) Quality of fabric (c) Design and colour (d) Brand (e) Comfort
(ii) How often do you use computers? (a) Daily (b) Two or three times a week (c) Once a week (d) Rarely (e) Never
(iii) Which newspapers do you read regularly? (a) The Times of India (b) The Hindu (c) Hindustan Times (d) Dainik Jagran (e) Other (please specify) (f) None
(iv) Rise in the price of petrol is justified. (a) Strongly agree (b) Agree (c) Neither agree nor disagree (d) Disagree (e) Strongly disagree
(v) Monthly income of your family: (a) Below ₹10,000 (b) ₹10,000–₹25,000 (c) ₹25,000–₹50,000 (d) ₹50,000–₹1,00,000 (e) Above ₹1,00,000
Each question gets four or more mutually exclusive options that cover all likely answers, as above.
Frame five two-way questions (with ‘Yes’ or ‘No’).
Answer
Answer
- Do you own a smartphone? Yes / No
- Do you travel to school by bus? Yes / No
- Do you read a newspaper daily? Yes / No
- Does your family own a car? Yes / No
- Do you use public transport at least once a week? Yes / No
Two-way questions allow only two answers (Yes/No), e.g. “Do you own a smartphone?”
Answer
State whether the following statements are True or False.
Answer
- There are many sources of data.
- Telephone survey is the most suitable method of collecting data, when the population is literate and spread over a large area.
- Data collected by investigator is called the secondary data.
- There is a certain bias involved in the non-random selection of samples.
- Non-sampling errors can be minimised by taking large samples.
Answer
- True. Data can be primary or secondary, from many agencies and publications. (Strictly, there are two kinds of source: primary and secondary.)
- False. When the population is literate and spread over a wide area, the mail survey is most suitable; a telephone survey needs telephone access and gives limited time.
- False. Data collected by the investigator are primary data.
- True. In non-random sampling the investigator’s judgement or convenience decides selection, which introduces bias.
- False. Taking larger samples reduces sampling errors, not non-sampling errors; non-sampling errors may even increase with larger samples.
- True (ii) False (iii) False (iv) True (v) False
What do you think about the following questions? Do you find any problem with these questions? Describe.
Answer
- How far do you live from the closest market?
- If plastic bags are only 5 per cent of our garbage, should it be banned?
- Wouldn’t you be opposed to increase in price of petrol?
- Do you agree with the use of chemical fertilisers?
- Do you use fertilisers in your fields?
- What is the yield per hectare in your field?
Answer
- Ambiguous/vague: the unit (km, metres, minutes) is not stated. Better: “What is the distance (in km) from your home to the nearest market? (a) Less than 1 km (b) 1–3 km (c) More than 3 km”.
- Leading question: the phrase “only 5 per cent” pushes the respondent towards “No”. Better: “Should plastic bags be banned?”
- Leading question with a negative construction; it suggests the expected answer. Better: “Do you favour the increase in petrol prices? Yes / No”.
- Too general: it does not say for which crop or purpose, and the answer depends on the respondent’s knowledge. It could be made more specific, or given a scale of agreement.
- This is a simple, clear two-way question; it has no problem. (It should, however, come before question (iv) in a logical order.)
- This may be difficult to answer accurately: farmers may not know the area in hectares or may not want to disclose yield; units should be stated (quintals per hectare) and the crop specified.
- vague units (ii) and (iii) leading (iv) too general (v) acceptable (vi) hard to answer precisely; units and crop not specified.
You want to do a research on the popularity of Vegetable Atta Noodles among children. Design a suitable questionnaire for collecting this information.
Answer
Answer
Questionnaire: Popularity of Vegetable Atta Noodles among children
- Name (optional): __________
- Age: (a) Below 6 years (b) 6–10 years (c) 11–14 years (d) Above 14 years
- Gender: Boy / Girl
- Do you eat noodles? Yes / No
- Have you tasted Vegetable Atta Noodles? Yes / No
- How often do you eat Vegetable Atta Noodles? (a) Daily (b) Weekly (c) Monthly (d) Rarely
- How do you like their taste? (a) Very good (b) Good (c) Average (d) Poor
- Which do you prefer? (a) Vegetable Atta Noodles (b) Maida noodles (c) Both equally
- Why do you eat them? (a) Taste (b) Healthy (c) Quick to cook (d) Advertisement (e) Parents’ choice
- Who decides which noodles to buy? (a) Myself (b) Parents (c) Others
- Is the price reasonable? Yes / No
- Would you recommend them to your friends? Yes / No
- Any suggestions to improve the product? __________
A short questionnaire of simple, ordered, mostly multiple-choice and yes/no questions on age, frequency, taste, preference, reasons and price.
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. What is the population and the sample size?
Answer
Answer
- Population = all the farms in the village = 200 farms.
- Sample size = the farms actually surveyed = 50 farms.
(Of the sample, 50 % = 25 farms grew only wheat.)
Population = 200 farms; sample size = 50 farms.
Give two examples each of sample, population and variable.
Answer
Answer
Population | Sample | Variable |
|---|---|---|
All students of a school | 50 students selected from the school | Height or marks of students |
All households in a city | 500 households selected from it | Monthly income or expenditure of households |
Population: all students of a school; all households of a city. Sample: 50 of those students; 500 of those households. Variable: marks/height; income/expenditure.
Which of the following methods give better results and why?
Answer
- Census (b) Sample
Answer
Sample generally gives better results in practice:
- It gives reasonably accurate information at much lower cost and in less time.
- Fewer units mean better-trained investigators can be used, and more detailed information can be collected, so non-sampling errors are smaller.
- Census is needed only when information about every unit is required (e.g. the population census), or when the population is small.
A sample, because it gives fairly accurate results at less cost and time, with fewer non-sampling errors; a census is needed only when every unit must be covered.
Which of the following errors is more serious and why?
Answer
- Sampling error (b) Non-Sampling error
Answer
Non-sampling error is more serious.
- Sampling error is the difference between the sample estimate and the true population value. It can be reduced by increasing the sample size, and it can be estimated.
- Non-sampling errors arise from mistakes in collecting data: measurement errors, wrong recording, non-response, biased selection, respondent bias. They are difficult to detect and measure, cannot be reduced by taking a larger sample, and occur in both census and sample surveys.
Non-sampling error, because it is hard to detect, cannot be reduced by a bigger sample, and affects both census and surveys.
Suppose there are 10 students in your class. You want to select three out of them. How many samples are possible?
Answer
Answer
Given: N = 10 students, n = 3 to be selected (order does not matter).
Formula: Number of samples
120 samples are possible.
Discuss how you would use the lottery method to select 3 students out of 10 in your class.
Answer
Answer
- Write the names (or roll numbers) of all 10 students on 10 separate slips of the same size, shape and colour.
- Fold the slips in the same way and put them in a box or bowl.
- Mix them thoroughly.
- Draw three slips one by one, without looking (without replacement).
- The students whose names appear on the three slips form the random sample.
Each student has an equal chance of being selected.
Write the 10 names on identical slips, fold and mix them in a box, and draw three slips blindly; those students form the sample.
Does the lottery method always give you a random sample? Explain.
Answer
Answer
Yes, provided the procedure is followed properly. A sample is random when every unit has an equal chance of being selected. In the lottery method this holds only if:
- the slips are identical in size, shape, colour and folding;
- they are thoroughly mixed; and
- the slips are drawn without looking and without any bias.
If slips differ (e.g. one is bigger or folded differently) or are not shuffled, the selection is no longer random.
Yes, as long as identical slips are well mixed and drawn blindly so that every unit has an equal chance.
Explain the procedure for selecting a random sample of 3 students out of 10 in your class by using random number tables.
Answer
Answer
- Give each of the 10 students a number from 01 to 10 (two-digit numbers, since 10 has two digits).
- Open a random number table and choose a starting point at random (any row and column).
- Read two-digit numbers from there, moving along a row or down a column.
- Select the students whose numbers appear first; ignore numbers above 10 (and 00) and any repeated numbers.
- Continue until three different students are selected.
For example, if the digits read are 27, 06, 81, 10, 64, 06, 03, the selected students are 06, 10 and 03.
Number the students 01–10, start anywhere in a random number table, read two-digit numbers, and pick the first three valid, non-repeated numbers between 01 and 10.
Do samples provide better results than surveys? Give reasons for your answer.
Answer
Answer
A sample survey is itself a kind of survey; the comparison is between a sample survey and a census (complete enumeration) survey.
Yes, samples often give better results
- A sample can provide reasonably reliable and accurate information at a lower cost and in less time.
- Fewer units mean better-trained investigators and more careful supervision, so non-sampling errors are lower; more detailed information can be collected.
- When the population is very large or units are destroyed by testing (e.g. testing the quality of bulbs), a sample is the only practical method.
However, a census is better when information about every unit is required and resources are available.
Yes; a well-chosen sample gives accurate results more cheaply and quickly, with fewer non-sampling errors than a complete (census) survey.
Topic checklist
- Primary and secondary data
- Preparing a questionnaire; good and bad questions
- Modes of survey and pilot survey
- Census and sample; random and non-random sampling
- Lottery method and random number tables
- Sampling and non-sampling errors
- Agencies collecting data in India