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Estimating Methods, Variability, and Sampling for Drop-Test Data

Appendix (Continued)

design graphic

Grid Spacing

Gpc data collected from a previous drop test, which used a grid with cups in a 10- by 10-foot spacing, were used for the following comparisons. The 10- by 10-foot spacing provided a data set that could be divided into subsets for cross validation. Two subsets were created with the points in a 20- by 10-foot spacing, and three subsets were created with the points in a 30- by 10-foot spacing. Figures 22 and 23 show examples of these subsets. Tables 10 to 14 display the cross validation tabular results. Figures 24 and 25 display the QQ-plots comparing distributions.

Figure 22—The original 10-foot spacing was increased
to 20 feet to evaluate sampling density.


Figure 23—The original 10-foot spacing was increased
to 30 feet to evaluate sampling density.



Table 10—First comparison of observed gpc (gallons per hundred square feet) values from a 10- by 10-foot spacing with predicted values from a 20- by 10-foot spacing. MAE is mean absolute error and MSE is mean squared error.
 
  TRUE Triangulation
(gpc)
Mean 1.534 1.509
Standard deviation 0.905 0.819
Minimum 0.037 0.068
1st quartile 0.950 0.962
Median 1.380 1.419
3rd quartile 2.008 2.052
Maximum 5.081 5.428
Correlation   0.905
n 319 319
Summary statistics for error distribution
  Triangulation
(gpc)
Mean 0.02483
Standard deviation 0.386
Minimum -1.856
1st quartile -0.144
Median -0.021
3rd quartile 0.150
Maximum 2.206
MAE 0.246
MSE 0.149
n 319


Table 11—Second comparison of observed gpc (gallons per 100 square feet) values from a 10- by 10-foot spacing with predicted values from a 20- by 10-foot spacing. MAE is mean absolute error and MSE is mean squared error.
 
  TRUE Triangulation
(gpc)
Mean 1.524 1.550
Standard deviation 0.922 0.805
Minimum 0.040 0.093
1st quartile 0.909 0.994
Median 1.412 1.411
3rd quartile 2.012 2.071
Maximum 8.183 4.060
Correlation   0.893
n 308 308
Summary statistics for error distribution
  Triangulation
(gpc)
Mean -0.02628
Standard deviation 0.416
Minimum -1.044
1st quartile -0.201
Median -0.035
3rd quartile 0.096
Maximum 4.122
MAE 0.241
MSE 0.173
n 308

Grid spacing continued...


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