The primary methods for data collection in quantitative studies are:. a) observations, scales, questionnaires, and physiological measures. b) physiological measures, scales, observations, and subjective methods. c) questionnaires, subjective surveys, rating scales, and focus groups. d) physiological measures, scales, interviews, and direct observations.

C- Questionnaires, subjective surveys, rating scales, and focus groups.

Explanation:

Primary methods of data collection in qualitative studies are usually questionnaires, experiments, correlation, focus group, rating scales and others.

Primary data can be collected in a number of ways however the most common techniques are self-administered surveys, interviews, field observation, and experiments.

Primary data collection is quite expensive and time consuming. Some of the quantitative data collection methods include various forms of surveys – online surveys, paper surveys, online polls, and systematic observations.