A chemical engineer assesses the quality of the plastic that is used in manufacturing billiard balls. Because higher elasticity is better, the engineer wants to determine whether either of two additives improves the elasticity of the plastic. The engineer prepares 10 samples with each of the two additives and 10 samples with no additive and measures the elasticity of each.
As part of the initial investigation, the engineer creates an individual value plot to compare the elasticity of the samples. The engineer adds mean symbols, confidence intervals, and mean connect lines to the plot to compare the differences between the group means. (A plot with confidence intervals is sometimes called an interval plot.)
Additive 1 appears to increase elasticity. Additive 2 may actually decrease elasticity. For samples that have no additive (0), the elasticity appears to be between additives 1 and 2. The variation within each group appears to be about the same.