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Unformatted text preview: plots Response of rats to cocaine 45 Measured behaviour 40 35 30 25 20 15 10 5 0 0 1 2 3 4 5 Dose Dose 12345 Measured behaviour 10 17 23 28 40 6 Showing correlations: Showing correlations: Scatterplots Response of rats to cocaine Measured behaviour 45 40 35 30 25 20 Line of best­fit 15 10 5 0 0 1 2 3 4 5 Dose Dose 12345 Measured behaviour 10 17 23 28 40 6 Relationships between variables Relationships between variables No relationship Relationships between variables Relationships between variables Linear Non­linear Relationships between variables Relationships between variables Positive Negative Relationships between variables Relationships between variables Monotonic (always positive or always negative) Non­monotonic (curvilinear) Pearson product­moment Pearson product­moment correlation coefficient ( r ) • Varies in magnitude between –1 and +1 +1 Perfect positive linear relationship ­1 Perfect negative lineage relationship 0 No relationship • +1 and –1 both have the same strength of correlation • (all points fit onto a straight line), but differ in the direction of correlation The value of r therefore contains 2 types of information – Strength of relationship – Direction of relationship Pearson product­moment correlation coefficient ( r ) 0.7 0.6 0.6 Test 2 0.8 0.7 r=0.97 1 0.9 0.8 Test 2 1 0.9 0.5 0.4 r=0.72 0.5 0.4 0.3 0.3 0.2 0.1 0.2 0.1 0 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 Test 1 0.8 1 0.7 0.6 0.6 Test 2 1 0.9 0.8 0.7 Test 2 1 0...
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