The effect of manganese (Mn) on wheat growth is examined in the article “Manganese Deficiency and Toxicity Effects on Growth, Development and Nutrient Composition in Wheat” (Agronomy J., 1984: 213–217). A quadratic regression model was used to relate height (cm) to

, with mM as the units for added Mn.

The accompanying data was read from a scatter diagram appearing in the article.

x 1.0 .4 0 .2 1.0 y 32 37 44 45 46 x 2.0 2.8 3.2 3.4 4.0 y 42 42 40 37 30 In addition,

, and .

a. Is the quadratic model useful for describing the relationship between x and y? [Hint: Quadratic regression is a special case of multiple regression with , and .] Apply an appropriate procedure.

b. Should the quadratic predictor be eliminated?

c. Estimate expected height for wheat treated with 10 mM of Mn using a 90% CI. [Hint: The estimated standard deviation of is 1.031.]