=+b. The observed values of stress were 91, 97, 108, 111, 114, 110, 112, 102, 98, and 91. Using the best-fit quadratic gave corresponding predicted values of 94.16, 98.87, 102.93, 109.07, 111.16, 113.36, 113.48, 104.22, 95.93, and 90.80, respectively. Calculate a quantitative assessment of the extent to which variation in observed stress values can be attributed to the approximate quadratic relationship between stress and strain.