Which method of collecting primary data is most suitable when the field of investigation is highly confidential and restricted? MCQ with Answer and Explanation

Explanation:
Sampling error arises because only a part of the population is surveyed.

Explanation:
Yule's Q = [(AB)(αβ) - (Aβ)(αB)] / [(AB)(αβ) + (Aβ)(αB)], requiring the four cell frequencies of a 2×2 table cross-classifying two dichotomous attributes.

Explanation:
Weighted indices assign weights (e.g., expenditure shares) to reflect the economic significance of items, providing a more realistic measure of overall change than simple indices that treat all items equally.