Updated NCERT Solutions for Class 11 Statistics Chapter 2: Collection of Data | Important Questions 2026-27
Welcome, students! This guide provides comprehensive notes and Updated NCERT Solutions for Class 11 Statistics Chapter 2: Collection of Data. We'll break down how data is gathered and why it's the crucial first step in any statistical study. Mastering this chapter is vital for scoring well in board and competitive exams.
Chapter at a Glance
Chapter 2: Collection of Data – Quick Reference
| Chapter Name | Collection of Data |
| Subject | Statistics (for Economics) |
| Board / Class | CBSE Class 11 |
| Target Year | 2026-27 |
| Important Topics | Sources of Data (Primary & Secondary), Methods of Collecting Primary Data (Personal Interview, Mailed Questionnaire, Telephone Interview), Census and Sample Survey, Qualities of a Good Questionnaire. |
| Difficulty Level | Easy |
| Exam Weightage | 4–6 Marks |
Learning Objectives
Understand the meaning and purpose of data collection.
Differentiate between primary and secondary sources of data.
Identify various methods used to collect primary data.
Evaluate the pros and cons of different data collection techniques.
Distinguish between the Census and Sample methods of survey.
Design a well-structured and effective questionnaire.
Appreciate the importance of a pilot survey before a large-scale study.
Key Concepts & Definitions
Full NCERT Solutions – All Exercise Questions
(i) Which of the following is the most expensive method of data collection?
- Telephone Interview
- Mailed Questionnaire
- Personal Interview
- Online Survey
Explanation: Personal interviews require trained investigators, travel, and significant time, making them the most expensive method.
(ii) Which of the following is the most time-consuming method of data collection?
- Telephone Interview
- Mailed Questionnaire
- Personal Interview
- Online Survey
Explanation: Conducting face-to-face interviews with a large number of people takes much longer than sending out emails or making quick phone calls.
(iii) Which of the following methods is most suitable for collecting data on a sensitive topic like alcohol consumption?
- Telephone Interview
- Mailed Questionnaire
- Personal Interview
- Observation
Explanation: Mailed questionnaires provide anonymity, which encourages respondents to give more honest answers on sensitive or personal topics without feeling judged.
(iv) Which of the following methods is prone to the highest non-response rate?
- Telephone Interview
- Mailed Questionnaire
- Personal Interview
- Schedule filled by enumerator
Explanation: Many people do not bother to fill out and return questionnaires received by mail, leading to a high rate of non-response.
(v) A good questionnaire should not have:
- Simple language
- A logical sequence of questions
- Ambiguous and leading questions
- Clear instructions
Explanation: Ambiguous questions confuse the respondent, and leading questions bias their answers, both of which should be strictly avoided in a good questionnaire.
- There is a certain amount of personal bias in the personal interview method. — True. The investigator's presence, way of asking questions, or reactions can influence the respondent's answers.
- The mailed questionnaire method has the lowest non-response rate. — False. The mailed questionnaire method typically has the highest non-response rate because respondents may ignore or forget to return the form.
- The census method is suitable for a survey with a large and diverse population. — False. The census method is extremely costly, time-consuming, and difficult to manage for a large and diverse population. The sample method is more suitable in such cases.
- Secondary data is generally more reliable and original than primary data. — False. Primary data is original and collected firsthand for a specific purpose, making it more reliable. Secondary data might be outdated, irrelevant, or collected with a different objective.
- A pilot survey helps in pre-testing the questionnaire. — True. A pilot survey is a crucial step to identify problems with question wording, instructions, or flow before conducting the main survey, thus ensuring better quality data.
| Basis of Difference | Census Method | Sample Method |
|---|---|---|
| Coverage | Includes every single unit of the population. | Includes only a representative part (sample) of the population. |
| Suitability | Suitable when the population size is small and not widely dispersed. | Suitable when the population size is very large and diverse. |
| Cost | Very expensive in terms of time, money, and manpower. | Relatively inexpensive and economical. |
| Time | Extremely time-consuming. | Less time-consuming. |
| Accuracy | Provides highly accurate and reliable results as every unit is surveyed. | Results are less accurate as they are estimations based on a sample. (Prone to sampling error). |
| Example | The Census of India, conducted every 10 years to count every person. | Exit Polls during elections, where a small group of voters is surveyed to predict the overall result. |
| Basis of Difference | Primary Data | Secondary Data |
|---|---|---|
| Originality | It is original data collected for the first time. | It is second-hand data that has already been collected by someone else. |
| Source | Collected directly from respondents through surveys, interviews, etc. | Obtained from published sources (reports, journals) or unpublished sources. |
| Cost & Time | Collection is expensive and time-consuming. | Collection is relatively cheap and quick. |
| Objective | Collected to meet a specific objective of the investigator. | Collected for some other purpose, may not perfectly suit the current study. |
| Reliability | More reliable and accurate as it is collected firsthand. | Less reliable; its accuracy depends on the agency that originally collected it. |
Which is more reliable and why?
Primary data is more reliable than secondary data. The reason is that it is collected by the investigator themselves for a specific, pre-defined purpose. The investigator has full control over the data collection process, ensuring that the information is relevant, accurate, and up-to-date for their particular study. In contrast, secondary data was collected for a different purpose and might be outdated or not entirely suitable for the current investigation.
Advantages of Personal Interviews:
- High Response Rate: People are less likely to refuse a face-to-face request, leading to a higher completion rate.
- Flexibility: The investigator can clarify ambiguous questions and even ask follow-up questions to get more detailed information.
- Use of Visual Aids: The investigator can use pictures, maps, or other visual aids to help the respondent understand the questions.
- Collection of Supplementary Information: The interviewer can observe the respondent's body language and living conditions, which can provide additional context.
- Suitable for All: This method can be used even if the respondent is illiterate.
Disadvantages of Personal Interviews:
- Expensive: It is the most costly method due to the need for travel, training of interviewers, and time involved.
- Prone to Personal Bias: The interviewer's personal beliefs or way of asking questions can influence the respondent's answers.
- Time-Consuming: Conducting interviews with a large number of people takes a significant amount of time.
- Limited Coverage: It is difficult to cover a large geographical area in a short period.
- Requires Trained Staff: The success of the interview depends on the skill and training of the interviewer. An untrained person may not be able to extract the correct information.
Extra Important Questions (for Board Exam 2026-27)
A respondent is a person who provides the data or answers the questions for a statistical investigation. They are the source of the information.
Two examples are:
- Reports and publications of the Government of India (e.g., Census of India, Economic Survey).
- Journals and publications of international organizations (e.g., World Bank, IMF reports).
It is necessary to pre-test a questionnaire (conduct a pilot survey) to:
- Check for any ambiguity or difficult wording in questions.
- Assess the time and cost involved in the actual survey.
- Ensure the instructions are clear to the respondents.
- Get an idea of the likely response rate.
A telephone interview is more suitable when:
- The survey needs to be completed quickly.
- The respondents are spread over a large geographical area.
- The budget for the survey is low.
The main difference lies in who fills the form. A questionnaire is filled by the respondents themselves. A schedule is filled by a trained enumerator (investigator) who asks the questions and records the answers from the respondent.
A good questionnaire is the foundation of a successful survey. Its qualities are:
- Limited Number of Questions: The questionnaire should be as short as possible. Too many questions can lead to respondent fatigue and non-response.
- Simplicity and Clarity: The language used should be simple, clear, and unambiguous. Avoid jargon and technical terms. Example: Instead of "What is your annual remuneration?", ask "What is your yearly income?".
- Logical Sequence: Questions should be arranged in a logical order, moving from general to specific. Example: Ask about car ownership before asking about the brand of the car.
- Avoid Personal and Sensitive Questions: If unavoidable, they should be asked at the end and framed politely to ensure the respondent's privacy.
- No Leading Questions: Questions should not suggest an answer. Example: Instead of "Don't you think morning walks are good for health?", ask "What is your opinion on morning walks for health?".
- Clear Instructions: Provide clear instructions on how to fill out the questionnaire.
- Pre-testing (Pilot Survey): The questionnaire should be tested on a small group before finalising.
- Attractive Layout: A neat and well-spaced layout makes it easier for the respondent to read and answer.
The Census method is a type of survey where data is collected from every single individual or unit in the population or universe under study. For example, if a college wants to know the average marks of its 500 students, it would collect marks from all 500 students.
Merits of the Census Method:
- High Accuracy and Reliability: Since every unit is studied, the results are highly accurate and free from sampling errors.
- Extensive Information: It provides detailed and extensive information about the population, covering many different characteristics.
- Suitability: It is highly suitable when the area of investigation is small and the units are heterogeneous (very different from each other).
Demerits of the Census Method:
- Very Costly: It requires a huge amount of money, manpower, and resources, making it extremely expensive.
- Time-Consuming: The process of collecting, organising, and analysing data from every single unit takes a very long time.
- Not Feasible for Large Populations: It is practically impossible to use this method if the population is infinitely large or spread over a vast geographical area.
- Requires Huge Manpower: A large team of trained enumerators is needed to conduct the survey.
For this research, the most suitable method would be the Personal Interview method, possibly conducted in small groups (focus groups) outside schools or in malls.
Justification:
- Target Audience: The target audience is school children. They may not be able to understand a written questionnaire properly or may not respond to mailed/online surveys. A personal interview allows the investigator to explain questions in simple terms.
- Sensory Feedback: The research is about taste. A personal interview allows the children to taste the chocolate on the spot and give immediate feedback. This is impossible with mailed or telephone methods.
- Observing Reactions: The investigator can observe the children's non-verbal reactions to the taste and packaging (e.g., excitement, dislike), which is valuable data.
- Flexibility: The interviewer can ask follow-up questions like "Why do you like this color?" or "What does this flavor remind you of?" to get rich, qualitative data.
Comparison with Other Methods:
- Mailed Questionnaire: Not suitable. The response rate would be very low, and children might need parental help, which could bias the answers. Also, tasting is not possible.
- Telephone Interview: Not suitable. It's difficult to engage children over the phone, and again, the crucial element of tasting the product is missing.
- Online Survey: While possible, it's hard to verify the respondent's age and ensure they are giving thoughtful answers. The sensory experience is also absent.
Therefore, despite being more expensive, the personal interview method is the only practical and effective choice for this specific research objective.
(a) Should the ministry use a Census or a Sample survey? Give a reason.
The ministry should use a Sample survey.
Reason: Conducting a census (surveying every single child in all 50 villages) would be extremely time-consuming and expensive, especially given the poor road network. A well-designed sample survey (e.g., randomly selecting 10-15 villages) would provide reasonably accurate results much more quickly and economically.
(b) Which method of data collection (Personal Interview, Mailed Questionnaire, Telephone) would be most appropriate here? Why?
The most appropriate method of data collection would be Personal Interviews using Schedules.
Reason:
- Low Literacy Levels: Since the literacy level is low, respondents would not be able to fill out a mailed questionnaire.
- Reliability: Personal interviews ensure that a trained enumerator can ask the questions correctly, verify vaccination cards if available, and record the answers accurately on a schedule. This is crucial for reliable health data.
- Lack of Infrastructure: Poor road networks make travel hard, but telephone networks might be even more unreliable in a remote district, ruling out telephone interviews.
(a) What is the source of data for the company in this case (Primary or Secondary)?
The source of data would be Primary Data, as the company is collecting the information for the first time for its specific purpose of improving the app.
(b) Suggest the most efficient data collection method and justify your choice.
The most efficient method would be an Online Survey/Questionnaire sent via email or as a pop-up within the app itself.
Justification:
- Speed: This is the fastest way to reach a large, geographically dispersed audience. The company can get feedback within a week as required.
- Cost-Effective: It is extremely cheap compared to any other method. There are no printing, postage, or interviewer costs.
- Target Audience: The respondents are premium customers of an online shopping company, which means they are tech-savvy and have internet access, making them ideal for an online survey.
- Data Processing: The responses are collected in a digital format, making analysis and report generation quick and easy.
Common Mistakes to Avoid
Exam Preparation Tips for 2026-27
Frequently Asked Questions (FAQs)
Master Collection of Data 📊
Mastering the Collection of Data is your first step towards becoming proficient in statistics. This chapter lays the groundwork for everything that follows—organisation, presentation, and analysis. We hope these Updated NCERT Solutions, important questions, and study tips help you excel. Good luck with your preparation for the Board Exam 2026-27!
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