Learning outcomes
- connect single-variable summaries with two-variable analysis
- understand why association matters
- identify possible variable-type pairs
- avoid confusing summary with relationship
Why move from one variable to two variables?
- Earlier weeks focused on describing one variable at a time.
- Now the goal is to ask whether two variables move together or differ across groups.
- study hours and marks
- gender and course preference
- department and attendance category
Meaning of association
- Association means one variable shows a pattern with another variable.
- It does not automatically mean one variable causes the other.
Three common cases
- two categorical variables
- two numerical variables
- one categorical and one numerical variable
Review connections
- frequency tables describe one variable
- charts visualize one variable
- mean and median summarize center
- dispersion summarizes spread
- association studies relationship between variables
Exam hints and traps
- Do not jump from “related” to “caused”.
- Variable type determines the right summary method.
- A single summary like mean cannot explain a relationship by itself.
Quick practice
- Is “hours of sleep” and “marks” a one-variable or two-variable situation?
- Name the variable types in “blood group” and “department”.
- Can two numerical variables be studied with a scatterplot?
Answer key
- Two-variable situation
- Both categorical
- Yes