Looking for Relationships… Trends, correlations and other scattered thoughts!
Scatter plots – looking for patterns
Inspect the Data…
Terminology… Time spent studying - Explanatory Variable Exam score – Response Variable Trend in the scatterplot: Exam performance increases with study Positive Association
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
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
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?
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.
In conlcusion… Read the summaries on pages 115-116 and 130-131 Try 2.15, 2.21, 2.33