Introductory Statistics for Economists
ECON 2500 – Winter 2011 – Xianghong Li
Chapter 2 – Looking at Data – Relationships – Jan 18
Topics of this Chapter
- Relationships between two variables.
- The two variables are measured on the same individuals (or subjects). E.g.
weight and height, GPA and mother’s education level.
Introduction: Associations between Two Variables
- When there is a casual relationship:
o Response variable: measures an outcome of a study.
o Explanatory variable: explains or causes changes in the response
o There may not be distinction of response vs. explanatory between two
variables, e.g. city and highway gas mileages for two-seater cars.
o Many explanatory-response relationships do not involve direct causation,
e.g. high school SAT scores and college grades.
- A scatterplot shows the relationships between two quantitative variables
measured on the same individuals.
- There may be no explanatory-response distinction between the two variables.
- If there is a distinction, always plot the explanatory variable on the horizontal axis
and response variable on the vertical axis.
- Overall pattern and striking deviations from that pattern.
- Describing the overall pattern by the form, direction a