Scatter Plots

Scatter Plots

• When two variables x and y have an association (or relationship), we say there exists a correlation between them. Alternatively, we could say x and y are correlated. To find such an association, we usually look at a scatterplot and try to find a pattern.

• Scatterplot (or scatter diagram) is a graph in which the paired (x, y) sample data are plotted with a horizontal x axis and a vertical y axis. Each individual (x, y) pair is plotted as a single point.

• One variable is called independent (X) and the second is called dependent (Y).

Example:

• Fig. 3.2.1 shows the scatter diagram.

• The pattern of data is indicative of the type of relationship between your two variables :

1. Positive relationship

2. Negative relationship

3. No relationship.

• The scattergram can indicate a positive relationship, a negative relationship or a zero relationship.

Advantages of Scatter Diagram

1. It is a simple to implement and attractive method to find out the nature of correlation.

2. It is easy to understand.

3. User will get rough idea about correlation (positive or negative correlation).

4. Not influenced by the size of extreme item

5. First step in investing the relationship between two variables.

Disadvantage of scatter diagram

• Can not adopt an exact degree of correlation.