Scatterplots & Correlation Coefficients: Fresh Take

  • Create scatterplots for bivariate data and answer questions from the graph.
  • Describe the trend of bivariate data.
  • Calculate the correlation coefficient and explain what it means.

Scatterplots

Scatterplots are used to illustrate the relationship between two quantitative variables.

The table of data presented below includes information collected from 18 grocery stores in San Antonio, Texas. The average household income (in thousands of dollars)[1] and the number of organic vegetables offered were collected in 2021 to explore this relationship.[2]

Store Location Average Household Income ($1000s) Number of Organic Vegetables Offered   Store Location

Average Household Income

($1000s)

 Number of Organic Vegetables Offered
S. Flores 71 36   Marbach Rd. 49 38
N. Rosillo St. 34 4   Babcock Rd. 66 84
Nogalitos St. 71 28   Wurzbach Rd. 87 61
Fredericksburg Rd. 49 31   W. Loop 1604 N. 78 56
Olmos 78 78   Bandera Rd. 59 62
N. New Braunfels Ave. 41 14   S. New Braunfels 50 44
Castroville 38 12   S.W. Military 48 26
Culebra Rd. 50 18   S. Zarzamora 56 29
S.E. Military Dr. 50 65   E. Basse Rd. 125 95

Let’s enter the data into our statistical tool to create a scatterplot.

Step 1: Locate the drop-down menu under Enter Data and select Your Own.

Step 2: Select the box titled Use ID Variable and name the ID Variable and the X and Y-Variables appropriately given the three columns in the data table.

Step 3: Complete the data table appropriately. Then select Submit Data (you may need to scroll down to see it) to create the scatterplot.

[Trouble viewing? Click to open in a new tab.]

Increasing and Decreasing Trends

A positive (or increasing) relationship means that an increase in one of the variables is associated with an increase in the other. A negative (or decreasing) relationship means that an increase in one of the variables is associated with a decrease in the other.  Note that not all relationships can be classified as either positive or negative.

The direction of the relationship can be positive, negative, or neither:

Scatterplot showing positive relationship. Dots on scatterplot are making an upwards trajectory.
Figure 1. A positive relationship is one where as values of X increase, values of Y also increase.
Scatterplot showing a negative relationship. Dots on scatterplot are making an downwards trajectory.
Figure 2. A negative relationship is one where as values of X increase, values of Y decrease.
Scatterplot showing neither positive nor negative relationship. Dots on the scatterplot form a U shape.
Figure 3. Some relationships may show neither a clear positive nor negative pattern.
  1. Income by Zip Code. (2021). https://www.incomebyzipcode.com/ ↵
  2. HEB. (2021). Shop by Department. https://www.heb.com ↵