Q.The data collected by questionnaires are __________.

Data gathered directly from respondents through questionnaires are primary data — option (b).

In the Tamil Nadu HSC Class-12 Economics (statistical methods) syllabus, data are classified by their source:

• Primary data are collected first-hand by the investigator for a specific purpose, using methods like direct interviews, questionnaires and schedules.
• Secondary data are already collected and published by someone else (government reports, journals, etc.). …

The word 'econometrics' was coined by Ragnar Frisch.

Econometrics is the branch that applies statistical and mathematical methods to economic data to test economic theories and estimate relationships. The Norwegian economist Ragnar Frisch coined the term 'econometrics' in 1926 and was a founder of the Econometric Society; he was also a co-recipient of the first Nobel Memorial Prize in Economic Sciences in 1969.

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'Statistics' is used both in the singular and the plural sense, so option (b) is correct.

In the introduction to statistical methods in the Tamil Nadu HSC Commerce syllabus, the word 'statistics' carries two meanings:

• Plural sense — statistics as data: it refers to numerical facts and figures collected systematically, e.g., statistics of population, prices or production. …

Secondary data is drawn from both published and unpublished sources, so option (d) is correct.

Secondary data is information already gathered and recorded by others, which the investigator reuses. Its sources are:

• Published sources — government reports, journals, newspapers, census reports, RBI bulletins, etc. …

Data collected by questionnaire is primary data.

Statistical data is of two kinds by source:

• Primary data — original data collected first-hand by the investigator specifically for the study, e.g. through questionnaires, interviews, direct observation or surveys. …