Correlation - Applied Statistics - Lecture Slides, Slides of Psychology

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Correlation

Correlation

• As one variable increases another variable increases or decreases
• Correlation may indicate a causal relationship
• For a causal relationship to exist it must have a relationship of correlation
• Correlation is indicative of a relationship

Other Relationships

• Positive – direct relationship between variables; as X increases so does Y; also indicated by a positive slope
• Negative – Inverse relationship between variables; as X increases Y decreases; also indicated by a negative slope

Other Relationships

• Perfect Relationship – Positive or negative relationship exists and all other points fall in line
• Imperfect Relationship – a relationship exists, but all points do not fall on the line - Perfect relationships are rare - Usually in the behavioral sciences, we deal with imperfect relationships

Correlation

• Looks at direction and degree of relationship
  • Direction – positive or negative
  • Degree – magnitude or strength of relationship

Correlation Coefficient

• Expresses a relationship quantitatively by showing degree and direction - Sign = positive or negative - Numeral = magnitude - Varies from +1(perfect positive relationship) to - (perfect negative relationship) - 0 indicates no relationship

Pearson r

2 2 2 2

X Y XY r N X Y X Y N N

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