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Chapter 2: Collection of Data

Sources of Data: Primary and Secondary

In statistical inquiry, data acts as the raw material. Based on the source of collection, data is classified into two types:

  1. Primary Data: Data collected originally for the first time by the investigator for a specific purpose. It is first-hand information.
  2. Secondary Data: Data that has already been collected by someone else and has passed through the statistical process.

Methods of Collecting Primary Data

  • Direct Personal Investigation: The investigator personally contacts informants.
  • Indirect Oral Investigation: Information is collected orally from third parties who are likely to possess the necessary information.
  • Information from Local Sources or Correspondents: Local agents report information continuously in their own manner.
  • Questionnaires and Schedules: Questionnaires are sent by mail or asked by enumerators to gather detailed responses.

Concepts of Sampling

Since studying an entire population (Census) is often time-consuming and expensive, statisticians use sampling. A sample is a subset of the population selected to represent the entire group.

  • Random Sampling: Every item in the universe has an equal chance of being selected (e.g., lottery method).
  • Non-Random Sampling: Items are selected based on the investigator’s judgment or convenience.

Important Sources of Secondary Data

  1. Census of India: Published by the Government of India every 10 years, it provides comprehensive demographic, social, and economic data.
  2. National Sample Survey Organisation (NSSO): Now part of the NSO, it conducts nationwide large-scale sample surveys on various socio-economic issues.

Competency-Based Questions

Case-Based Question

Q1. A researcher wants to understand the impact of online education on the mental health of Grade 11 students in a specific school. If the researcher designs a questionnaire and distributes it to a randomly selected group of 50 students from that school, identify: (a) The type of data being collected (Primary or Secondary). (b) The method of data collection being utilized.

Answer: (a) The data collected is Primary Data, as it is originally gathered by the researcher for this exact study. (b) The method of data collection is the use of Questionnaires combined with Random Sampling, since the researcher selected 50 students randomly and gathered responses directly.

Analytical Questions

Q2. Differentiate between a Census and a Sample Survey. Why might the NSSO prefer sample surveys over a complete census for tracking employment figures annually?

Answer:

  • Census involves collecting data from each and every unit of the population, whereas a Sample Survey involves collecting data from a representative subset of the population.
  • The NSSO prefers sample surveys for annual tracking because conducting a complete census every year is highly resource-intensive, time-consuming, and practically impossible at a national scale. Sample surveys provide swift and reasonably accurate estimates, allowing the government to adapt its employment policies proactively.