312 IAC 25-6-61 Revegetation; statistical methodology

Sec. 61. (a) The methods set forth in this section are used to evaluate the success of revegetation pursuant to section 59 of this rule using the sampling techniques under section 60 of this rule. (b) The minimum number of observations for the area under evaluation shall be determined as provided under this subsection as follows: (1) Except as provided in subdivisions (2) through (3), the following table is used to determine the required minimum number of observations: Size of Area Under Evaluation(In Acres) Crop Minimum Number of Observations Corn 0–39 8 40–279 12 280–639 16 640 or more 28 Soybeans 0–39 10 40–279 12 280–639 16 640 or more 26 Wheat and Oats 0–39 6 40–279 8 280–639 10 640 or more 14 Sorghum 0–39 10 40–279 16 280–639 28 640 or more 40 Mixed Hay 0–39 5 40–279 10 280–639 20 640 or more 20 + 1 additional sample for each 35 acres in excess of 640 acres (2) If any two (2) observations vary by more than fifteen percent (15%), the director may increase the minimum number of observations required by the table in subdivision (1). If additional samples are required, the formula in subsection (e) shall be used to determine that the number of observations evaluated is sufficient. (3) A statistical analysis of the result obtained from the area under evaluation shall be performed using the method from subsection (c) or (d). If there are apparent discrepancies between the submitted yield derived from random sampling and yield estimates derived by the director, the operator may be required to harvest specific fields in their entirety. (c) Sampling results shall be analyzed and the following statistical parameters determined: (1) Sample mean (average): Where: ΣXi = The sum of the individual observation values. N = The number of observations. (2) Mean deviation squared: (3) Degree of freedom: d = N - 1 (4) Sample standard deviation: (5) t-value: Where: T = Desired target yield. The calculated t-value is compared with the value associated with the appropriate degree of freedom (d) in the following table to determine if the standard has been met. The calculated t-value must be less than or equal to the t-value derived from the table to demonstrate that the actual yield has achieved the standard with a ninety percent (90%) or greater statistical confidence. Degree of Freedom t-value 1 3.078 2 1.886 3 1.638 4 1.533 5 1.476 6 1.440 7 1.415 8 1.397 9 1.383 10 1.372 11 1.363 12 1.356 13 1.350 14 1.345 15 1.341 16 1.337 17 1.333 18 1.330 19 1.328 20 1.325 21 1.323 22 1.321 23 1.319 24 1.318 25 1.316 26 1.315 27 1.314 28 1.313 29 1.311 30 1.310 40 1.303 60 1.296 120 1.289 ∞ 1.282 (d) Other statistical methods may be approved by the director. (e) To determine if the number of samples is sufficient, the following formula will be used: Number of samples required: Where: s = Sample standard deviation. X̄ = Mean. The formula set forth in this subsection prescribes an interactive method in which the number of required samples is dependent upon the variation between the samples. Once the minimum number of samples is obtained, the appropriate information is substituted into this formula to determine if a sufficient number of samples were evaluated given the variation in the data. The collection of additional random samples, together with reapplication of the formula may, depending upon the overall consistency in observations, change the required number of samples as data collection progresses. In general, fewer samples are required if there is greater consistency among samples.