散布図

Bivariate data consists of quantitative information on two variables, such as house prices and ground area. One variable acts as the independent variable (the cause), while the other is the dependent variable (the response). Scatter plots visualize this relationship by plotting independent variables on the X-axis and dependent variables on the Y-axis, revealing patterns between the two variables.

To construct a scatter plot, place the independent variable along the X-axis and the dependent variable along the Y-axis. Mark each data point corresponding to paired values. Then draw a best fit line such that approximately equal numbers of points fall above and below it. This line helps identify the correlation pattern between the two variables.

Positive correlation occurs when an increasing trend appears in a scatter plot, meaning high values of one variable occur with high values of the other variable. For example, as ground area increases, house prices rise. The points cluster around an upward-sloping line, showing that the two variables move together in the same direction.

Negative correlation appears as a decreasing trend, where high values of one variable occur with low values of the other. No correlation exists when points show no clear pattern or trend, such as when all points fall on a horizontal line. Observing the overall pattern and any deviations helps determine the strength and direction of the relationship.

The best fit line is drawn through scattered points such that approximately equal numbers of data points lie above and below it. This line reveals the overall trend and direction of the relationship between variables. The closeness of points to this line indicates the strength of the linear relationship between the two variables.

The strength of a relationship is determined by observing how closely the data points cluster around a line or function. Points tightly grouped near the best fit line indicate a strong relationship, while scattered points suggest a weaker relationship. Understanding frequency distribution concepts helps contextualize how data concentration reflects relationship strength.

A scatter plot is the most common and easiest way to display relationships between two variables because it visually shows the direction and pattern of association. It allows you to quickly identify whether variables are positively correlated, negatively correlated, or unrelated. Scatter plots also reveal the overall pattern and highlight any unusual deviations in the data.