Ind. Admin. Code tit. 312, r. 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:

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

(1) Except as provided in subdivisions (2) through (3), the following table is used to determine the required minimum number of observations:
(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.

(1) Sample mean (average):
Where: ΣX_i = 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:
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.

Where:	ΣX_i	=	The sum of the individual observation values.
	N	=	The number of observations.

Where: T = Desired target yield.

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.

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.

(Natural Resources Commission; 312 IAC 25-6-61; filed Jun 21, 2001, 2:53 p.m.: 24 IR 3540, eff Dec 1, 2001; readopted filed May 29, 2007, 9:51 a.m.: 20070613-IR-312070146RFA; readopted filed Sep 19, 2013, 10:12 a.m.: 20131016-IR-312130125RFA; readopted filed Mar 26, 2019, 3:40 p.m.: 20190424-IR-312190011RFA; readopted filed Mar 25, 2025, 9:50 a.m.: 20250423-IR-312240574RFA)