**Question:** The scatter plot is used to display

A. Relationship between two numerical variables
B. Relationship between a categorical variable and a numerical variable
C. Relationship between three or more numerical variables
D. Relationship between two categorical variables

**Core Concept:** A scatter plot is a type of graphical representation used to visualize the relationship between two numerical variables. Each data point in the plot represents a single observation, and the position of the point reflects the values of the two variables being compared.

**Why the Correct Answer is Right:** A scatter plot is right for displaying the relationship between two numerical variables because it allows for easy visualization of the correlation between the two variables. By plotting the data points, one can observe the distribution, pattern, and strength of the relationship between the variables.

**Why Each Wrong Option is Incorrect:**

A. Relationship between two numerical variables: This is the correct use of a scatter plot, as mentioned above.
B. Relationship between a categorical variable and a numerical variable: A scatter plot is not suitable for categorical variables, as these cannot be represented numerically. Instead, appropriate graphical representations, such as a bar chart or pie chart, are used for categorical variables.
C. Relationship between three or more numerical variables: While multiple scatter plots can be displayed side-by-side to visualize the relationships among three or more numerical variables, a single scatter plot is not suitable for this purpose.
D. Relationship between two categorical variables: As mentioned above, categorical variables should be represented using appropriate graphical representations, such as a bar chart or pie chart.

**Clinical Pearl:** When analyzing scatter plots, one should carefully examine the line of best fit, which can provide insights into the strength, direction, and slope of the relationship between the two variables. A positive slope indicates a direct relationship, while a negative slope indicates an inverse relationship. A slope of zero suggests no relationship between the variables.

**Correct Answer:** A. Relationship between two numerical variables