Longitudinal Study and Readership Surveys
What is Longitudinal Study?
A longitudinal study is a correlational research study that involves repeated observations of the same variables over long periods of time — often many decades. It is a type of observational study. Longitudinal studies are often used in psychology to study developmental trends across the life span, and in sociology to study life events throughout lifetimes or generations. The reason for this is that unlike cross-sectional studies, in which different individuals with same characteristics are compared, longitudinal studies track the same people, and therefore the differences observed in those people are less likely to be the result of cultural differences across generations.
Give some real life examples where this method of research is being used?
Readership surveys (e.g. IRS) and Audience measurement techniques such as TRP are very common examples of the studies where this method of research is being used.
What is India’s Readership Survey (IRS)? How is it related to Longitudinal Study?
Modeled on internationally accepted annual sample spread, the IRS is the largest continuous readership research study in the world with an annual sample size exceeding 2.56 lakh respondents. It is conducted by MRUC (Media Research Users Council).
- The universe for IRS has been defined as the total resident urban and rural population of India aged 12 years and over.
- The survey excludes the off-shore territories such as Lakshadweep and Andaman & Nicobar Islands, North Eastern States (except Assam) and J&K are also excluded from the survey.
- The annual sample spread exceeds 2.56 lac respondents with continuous fieldwork spread across 10 months of the year.
- Sample allocated proportionate to 12 years+ Universe of a geographic unit.
- All 1 Lakh+ towns are sampled.
- All publication towns and districts are sampled in the four rounds.
- Remaining towns and non-publication districts are randomly sampled.
- Rural Sampling: Once a district is selected, 2 Talukas from the district are randomly sampled.
Universe Projection and Weighting:
- The IRS data is weighted to the census universe.
- Since the Census is conducted every ten years, the estimated population for any given date is calculated by using the growth rate in between two census points.
- Projection of Universe = the midpoint date of the Field work period. E.g. for FW period Jan to December the Population of India is projected to June using CDGR. (Cumulative Daily Growth Rate)
- Universe projections of over 1000 sub units is accrued to arrive at the All India Universe.
- Each weighting unit is divided into a number of weighting cells to create a weighting matrix for projecting the data.
Household and Individual Selection:
- The first Household in a cluster is randomly selected based on the electoral rolls
- Remaining Households selected using Right Hand Rule
- Individual selection made using Kish grid
- Kish grid designed to maintain age X gender proportion in the sample.