PSY 250 Lecture Notes - Lecture 9: Pearson Product-Moment Correlation Coefficient, Twin, Francis Galton
Document Summary
Experimental research: looks for general laws that apply to everyone: want min. differences. Interested in (manipulate variables) that influence all individuals in some systemic way. Correlational research: look for ways in which people differ from each other. Discovered co-relations btw heights of parents & children. Regression to the mean: taller than avg patterns tended to have tall children, but not quite as tall as parents. Positive correlation: higher scores on 1 variable associated with higher scores on a 2nd variable. Negative correlation: higher scores on 1 variable associated with lower scores on a 2nd variable. Note that -1 & +1 are virtually impossible in real life. Indicates the strength and direction of a correlation. Can be calculated for either interval or ratio scale data. In curvilinear relationships, r will be close to 0 e. g. in an inverted u-shaped relationship. Left half"s a strong positive correlation & right half"s a strong negative correlation. Important to have a wide range of scores.
