Unit 5: Getting Started with Correlations & Scatterplots

Concepts to review from earlier unitsSquares and Square roots (basic math)Order of operations (basic math)Summation notation (Σ)Concept of varianceLevels (Scales) of Measurement

After this module, you will be able to…Understand correlation coefficients Measures of strength of relationshipMeasures of direction of relationshipUnderstand scatterplots as representations of the distribution of two variables measured on the same casesEstimate correlations from scatterplotsUse Excel to compute Pearson correlationsExplain the difference between correlation and causation

Scatterplots plot individuals according to their scores on two variables

If the two variables are related, a pattern is visible in the data.As X increases, Y may also increaseAs X increases, Y may decreaseIf X is unrelated to Y,the scatterplot has aball shapeIt is possible for X and Y to have a non-linear relationship (studied in advanced statistics)

Pearson correlation coefficient If r = 0.00, there is no relationshipIf r = +1.00 or -1.00, there is a perfect relationship.Y can be predicted exactly, based on X.This is very rare.Correlations that are not perfect (not 1.00 or -1.00)measure the strength of relationship between two variables, from very weak to very strong.Some online games teach you to recognize the general strength of a relationship from a scatterplot.

Equation for the correlation coefficient looks daunting:DON’T FAINT!!When broken down into its parts, it is manageableOne short video shows you how to solve it step by step In Excel, it’s just one function: CORREL

Uses of correlationsCorrelations are useful to describe relationships among variables.In Unit 6, correlations are used to construct indexesfrom data on several variables, such as:Intelligence TestsPersonality TestsAPGAR scale for newbornsMarital happiness measuresMeasures of financial strengthDow Jones Stock Index

Unit 5: Getting Started with Correlations & Scatterplots