Quantitative Aptitude · Statistical Description of Data

Collection and Types of Data for CA Foundation

Updated 1 October 2026 · Fact-checked

Statistical data are numerical facts collected for study. Primary data are collected fresh by the investigator for a specific purpose, using methods like interviews, questionnaires and observation. Secondary data already exist, collected by someone else, and come from published or unpublished sources. To solve questions, ask who collected the data and for what purpose.

Understand Collection and Types of Data

Statistical data are facts expressed in numbers that are collected, organised and analysed to draw conclusions. A single number with no context is not useful data. A set of marks, prices or sales figures that you can compare is.

Data are classified by their source. Primary data are collected by you (or your organisation) for the first time, for the problem at hand. They are original and fit your purpose, but collecting them costs time, money and effort. Secondary data were already collected by someone else for another purpose, and you are only using them. They are cheaper and quicker, but may not fit your need exactly.

The same data can be primary for one person and secondary for another. A census officer who counts households collects primary data. A student who uses the published census report uses secondary data.

Primary data methods include direct personal investigation, indirect oral investigation (asking persons who know about the matter), information from local sources or correspondents, mailed questionnaires, questionnaires filled by enumerators, and observation. Each has a trade-off. Direct personal investigation is accurate but suits only a small area. Mailed questionnaires cover a wide area cheaply but often get low response.

Secondary data come from published sources (government reports, RBI publications, journals, newspapers, reports of trade bodies and international bodies) and unpublished sources (records kept by firms, research scholars' papers, and similar internal material). Before using secondary data, check how reliable, suitable and adequate they are.

Key formulas to remember

Primary data: Primary data = original data collected first-hand for the present purpose; Methods: direct personal investigation, indirect oral investigation, local sources, mailed questionnaire, enumerator-filled schedule, observation.
Secondary data: Secondary data = data already collected by others and now reused; Sources: published (government, international bodies, journals, trade reports) and unpublished (internal records).
Suitability check for secondary data: Check reliability, suitability and adequacy before use; Data may be accurate yet unsuitable if definitions, units or time period differ from your need.
Census vs sample: Census = every unit studied; Sample = a part of the units studied; Census is more complete but costly and slow. Sampling is faster and cheaper but carries sampling error.

How to solve Collection and Types of Data questions

Most questions ask you to label data as primary or secondary, match a method or source, or pick the best method for a situation. Use this order.

1Read the statement and find who collected the data.
2Ask whether the data were collected for the present study or taken from an earlier one.
3If collected fresh by the investigator, label it primary. If reused from existing records or reports, label it secondary.
4For method questions, match the key phrase: face-to-face means direct personal; asking third parties means indirect oral; post means mailed questionnaire; watching behaviour means observation.
5For situation questions, check area size, cost, time and accuracy needed. Wide area with low budget suggests mailed questionnaire. Small area with high accuracy suggests direct personal investigation.
6Eliminate options that contradict the definition, then pick the one that fits all the facts.

Quickest way: Who collected it? Why?

When to use it: Use this for any one-line MCQ asking you to classify data or match a method or source.

Underline the collector in the question: 'the investigator himself' points to primary, 'published by' points to secondary.
Spot keywords: questionnaire, interview, observation, survey mean primary. Report, journal, website, records, census publication mean secondary.
Remove options that mix the two categories wrongly.
If two options still look right, choose the one that fits the exact purpose stated.
Skip only if you cannot decide in about 30 seconds. Wrong answers cost 0.25 marks.

Common mistakes in Collection and Types of Data

Calling government census data primary for every user.
Students link the word 'census' with first-hand collection.
Fix: Primary or secondary depends on the user. The census office collects primary data. Anyone using the published report uses secondary data.
Treating secondary data as always less accurate.
Students think original means better.
Fix: Secondary data can be very reliable, for example from official sources. The issue is suitability for your purpose, not automatic inaccuracy.
Mixing up direct personal investigation and indirect oral investigation.
Both involve talking to people.
Fix: In direct personal investigation you meet the source of information yourself. In indirect oral investigation you ask other people who know about the matter.
Placing internal firm records under published sources.
Students assume anything on paper is published.
Fix: Records kept inside an organisation and not released publicly are unpublished sources.
Assuming mailed questionnaires give high response.
They cover a wide area, so students assume good results.
Fix: They are cheap and wide-reaching but often get low response and need literate respondents.
Ignoring the purpose when judging secondary data.
Students focus only on the source's reputation.
Fix: Always check whether definitions, units and time period match your need.

Worked examples

Example 1

A researcher uses the annual report published by a trade association to study industry sales. The data used are: (a) primary data (b) secondary data (c) neither primary nor secondary (d) both primary and secondary data

Show the solution

Find who collected the data: the trade association, not the researcher.
The data were collected earlier and are now being reused.
So for the researcher, the data are secondary.
The report is a published source.

Answer: (b) secondary data

Example 2

A company wants opinions from customers spread across many states at low cost, and can accept some non-response. Which method is most suitable? (a) Direct personal investigation (b) Observation (c) Mailed questionnaire (d) Census of all units by personal visit

Show the solution

The area is wide and the budget is low.
Direct personal investigation and a personal-visit census are costly and slow over many states, so (a) and (d) fail.
Observation records behaviour and does not collect stated opinions well, so (b) does not fit.
Mailed questionnaires reach many people cheaply, and the question accepts non-response.

Answer: (c) Mailed questionnaire

Example 3

Which of the following is an unpublished source of secondary data? (a) RBI bulletin (b) Government economic survey (c) Internal sales records of a firm kept for its own use (d) Newspaper report

Show the solution

Published sources are made available to the public, such as bulletins, surveys and newspapers.
So (a), (b) and (d) are published.
Internal records kept by a firm for its own use are not released publicly.
These are unpublished sources, and they are secondary when used by someone other than the original recorder.

Answer: (c) Internal sales records of a firm kept for its own use

Exam tips

Most questions are direct definition or matching items, so learn the two definitions and the list of methods and sources word for word.
Read the question for the collector and the purpose. These two clues settle most classification questions.
In situation questions, weigh area, cost, time and accuracy before choosing a method.
Watch for words like 'always' and 'only' in options. Rules about data types usually have exceptions.
This is a quick-scoring topic, so attempt every question you are sure of and avoid guessing blindly because of the 0.25 negative marking.

Practice questions from Statistical Description of Data

Collection and Types of Data: frequently asked questions

What is the difference between primary and secondary data?

Primary data are collected first-hand by the investigator for the present purpose. Secondary data were collected earlier by someone else and are reused. The key test is who collected the data and why.

What are the methods of collecting primary data?

The main methods are direct personal investigation, indirect oral investigation, information from local sources or correspondents, mailed questionnaires, and questionnaires filled by enumerators. Observation is also used. Each differs in cost, coverage and accuracy.

What are the sources of secondary data?

They are published sources such as government reports, international bodies' publications, journals, newspapers and trade association reports. Unpublished sources include internal records of firms and research papers not made public.

Can the same data be both primary and secondary?

Yes, depending on the user. The person who collects it first-hand has primary data. Anyone who later uses the collected data has secondary data.