Types and Sources of Data
Definition: Statistical data are numerical facts collected for a purpose. By source they are primary (collected first-hand by the investigator) or secondary (already collected by someone else and reused).
Primary vs Secondary
- Primary data — original, collected for the current study (surveys, direct interviews, questionnaires, observation). More reliable but costly and slow.
- Secondary data — from published sources (census reports, government publications, journals). Cheap and quick, but may not fit exactly and needs scrutiny for reliability.
Methods of Collecting Primary Data
Direct personal interview, indirect oral investigation, mailed questionnaires, schedules sent through enumerators, and telephone interviews.
Real-world example: A researcher surveying households directly collects primary data; using the national Census figures for the same area is using secondary data.
Solved Examples: Data Sources
Example 1. Data collected first-hand by an investigator for their own study is called:
- Primary data.
Example 2. Census reports used by a researcher for a new study are an example of:
- Secondary data.
Example 3. Which method uses enumerators to fill schedules at the respondent's location?
- Schedules through enumerators (a primary-data method).
⚡ Speed Tricks & Shortcuts
- Primary = collected first-hand for this study; Secondary = already collected by others.
- Census reports/journals used later are secondary data.
- Primary is costlier but more reliable.
Calling census reports primary data — once reused, published data is secondary.
Primary and Secondary Data — Revision Notes
Quick-revision notes for Primary and Secondary Data — the must-know points for SSC CGL Tier-I/II.
- Primary data is collected first-hand by the investigator for a specific purpose (original data).
- Secondary data is already collected by someone else and reused (e.g. census reports).
- Primary data collection methods: direct interview, questionnaire, observation, telephonic survey.
- Secondary sources: government publications, journals, reports, and websites.
- Primary data is more reliable/accurate but costlier and time-consuming; secondary is cheaper but needs scrutiny.
- Data can be quantitative (numeric) or qualitative (attributes).
Primary and Secondary Data — Flashcards (SSC CGL)
Cover the answer, recall, then check. 6 cards on the must-know Primary and Secondary Data facts for SSC CGL.
Q1. Define primary data.
A1. Data collected first-hand by the investigator for a specific purpose.
Q2. Define secondary data.
A2. Data already collected by others and reused.
Q3. Give two methods of collecting primary data.
A3. Direct interview and questionnaire (also observation).
Q4. Which is generally more reliable, primary or secondary data?
A4. Primary data (collected directly for the purpose).
Q5. Give an example of a secondary data source.
A5. Government census reports or published journals.
Q6. What are the two broad types of data by nature?
A6. Quantitative (numeric) and qualitative (attributes).