A time series in which the data of only one variable vary over time is called
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Univariate time series
A univariate time series records the values of only one variable as they change over time, for example the temperature of a place noted every hour.
Why the other options are incorrect
Option (1) Multivariate time series — Incorrect. A multivariate time series records several variables and how they vary over time.
Option (2) Pooled data — Incorrect. Pooled data combine time series data and cross-sectional data.
Option (4) Cross-sectional data — Incorrect. Cross-sectional data are collected for one or more variables at the same point in time, not over time.