What is a Scatter Plot?
A scatter plot displays individual data points on a two-dimensional plane, with X and Y coordinates representing two numeric variables. Each point represents one observation, making scatter plots the go-to chart for exploring relationships, correlations, and patterns between paired variables.
Scatter plots are foundational in regression analysis, machine learning feature exploration, and any domain where understanding how one variable relates to another is key — from economics (income vs. education) to biology (dosage vs. response) to business (advertising spend vs. sales).
Interpreting Patterns
- Upward trend = positive correlation. As X increases, Y tends to increase (e.g., study hours vs. exam scores).
- Downward trend = negative correlation. As X increases, Y tends to decrease (e.g., exercise frequency vs. resting heart rate).
- Random cloud = little to no correlation. The variables appear independent of each other.
- Curved pattern = non-linear relationship. The variables are related but not in a straight-line fashion — consider transformation or non-linear modeling.
- Clusters or gaps = distinct subgroups or missing data ranges worth investigating.
Frequently Asked Questions
How do I interpret the correlation in my scatter plot?
How many data points are recommended for a scatter plot?
What do I enter in the X and Y input fields?
Key Terms
- Correlation
- Measures the strength and direction of the linear relationship between X and Y.
- Independent Var (X)
- The variable that is manipulated or controlled.
- Dependent Var (Y)
- The variable that is measured or observed.
- Regression Line
- A best-fit line through the scatter points, showing the trend.
Computation Method
- Quartiles are calculated using linear interpolation (method 7 from Hyndman & Fan, 1996), consistent with Python's NumPy and pandas defaults.
- Outlier detection uses the Tukey fences method: lower fence = Q1 − 1.5 × IQR, upper fence = Q3 + 1.5 × IQR.
- Chart scaling caps the display axis at the upper fence value so the visualization remains clear even when extreme outliers are present.
References
- Hyndman, R. J. & Fan, Y. (1996). “Sample Quantiles in Statistical Packages.” The American Statistician, 50(4), 361–365.
- Tukey, J. W. (1977). Exploratory Data Analysis. Addison-Wesley.