=+13.29 ● ▼ The authors of the article “Age, Spacing and Growth Rate of Tamarix as an Indication of Lake Boundary Fluctuations at Sebkhet Kelbia, Tunisia” (Journal of Arid Environments [1982]: 43–51) used a simple linear regression model to describe the relationship between y 5 vigor (average width in centimeters of the last two annual rings) and x 5 stem density (stems/m2

). The estimated model was based on the following data. Also given are the