1. Looking for Relationships…
Trends, correlations and other scattered thoughts!

2. Scatter plots – looking for patterns

3. Inspect the Data…

4. Terminology… Time spent studying - Explanatory Variable
Exam score – Response Variable
Trend in the scatterplot:
Exam performance increases with study  Positive Association

5. Correlation
CO – Relation: two variables that may (or may not) change in a coordinated way:
If “A” goes up whenever “B” goes up then there is a positive correlation
If “A” goes down whenever “B” goes up then there is a negative correlation
“A” is as like to go up as down whenever “B” goes up then there is no correlation

6. Quantifying Correlation…
Since standard deviation measures spread in a data set it makes sense that it is involved in assessing correlation
“r” is the symbol used to denote correlation

7. Exam Score vs Studying…
Positive correlation
r = 0.442
Is this a “strong correlation”?
Does time spent studying explain performance:
Completely?
Partially?
Not at all?

8. Caution: Correlation does NOT imply Causation!
Correlation is only a mathematical relationship between two sets of numbers – be careful not to fall into the “causation trap”.
Read page 128 carefully!
If there is a causal relationship between two variables then you need to supply that link – the numbers don’t do it for you.

9. In conlcusion… Read the summaries on pages 115-116 and 130-131
Try 2.15, 2.21, 2.33