NIST/ITL StRD Dataset Name: Rat42 (Rat42.dat) File Format: ASCII Starting Values (lines 41 to 43) Certified Values (lines 41 to 48) Data (lines 61 to 69) Procedure: Nonlinear Least Squares Regression Description: This model and data are an example of fitting sigmoidal growth curves taken from Ratkowsky (1983). The response variable is pasture yield, and the predictor variable is growing time. Reference: Ratkowsky, D.A. (1983). Nonlinear Regression Modeling. New York, NY: Marcel Dekker, pp. 61 and 88. Data: 1 Response (y = pasture yield) 1 Predictor (x = growing time) 9 Observations Higher Level of Difficulty Observed Data Model: Exponential Class 3 Parameters (b1 to b3) y = b1 / (1+exp[b2-b3*x]) + e Starting Values Certified Values Start 1 Start 2 Parameter Standard Deviation b1 = 100 75 7.2462237576E+01 1.7340283401E+00 b2 = 1 2.5 2.6180768402E+00 8.8295217536E-02 b3 = 0.1 0.07 6.7359200066E-02 3.4465663377E-03 Residual Sum of Squares: 8.0565229338E+00 Residual Standard Deviation: 1.1587725499E+00 Degrees of Freedom: 6 Number of Observations: 9 Data: y x 8.930E0 9.000E0 10.800E0 14.000E0 18.590E0 21.000E0 22.330E0 28.000E0 39.350E0 42.000E0 56.110E0 57.000E0 61.730E0 63.000E0 64.620E0 70.000E0 67.080E0 79.000E0