How Facilities Were Selected for

Speciated Mercury Emissions Testing

"Using a Table of Random Numbers," is the title of a short chapter in Myles Hollander and Frank Proschan's book The Statistical Exorcist: Dispelling Statistics Anxiety (pp. 89-93). The contents of this chapter explain what a random number table is, while referencing the "10,000 Random Digits" table found in Appendix I of the textbook, and how this table is used to generate a random sample representative of the population of interest. In the summary of this chapter on p. 92, Hollander and Proschan make the following three key points:

1.	A table of random numbers is very useful for selecting a representative sample from a population.

2.	The essential features of a table of random numbers are:

A.	The equal-likelihood feature--the chance that any particular one-digit entry is a 0 is 1/10, the chance that it is a 1 is 1/10, and so forth.

B.	The mutual independence feature--knowing some or all of the entries in the table except for the digit in question does not change the chances affecting the digit in question, that is, the chance that it is a 0 remains 1/10, the chance that it is a 1 remains 1/10, and so on.

3.	When all possible samples of a given size are equally likely to be selected, such sampling is called simple random sampling.

The "10,000 Random Digits" table found in Appendix I of the Hollander and Proschan text was used to select those plants that will be performing speciated mercury emissions testing at the inlet and outlet of the last emission control device installed under the Information Collection Request (ICR) for the Electric Utility Steam Generating Unit Mercury Emissions Information Collection Effort. Based on the general generating unit information from all known coal-fired electric utility steam generating units provided to the U. S. Environmental Protection Agency (EPA) under the aforementioned ICR, each generating unit was alphabetically listed (by plant name) within the previously defined categories found in Part B of the Supporting Statement for OMB Form 83-I. Due to information acquired about some facilities burning blends of coal types, which was not previously allowed in the defined categories, several additional categories were developed to accommodate these blending practices.

As stated in Part B of the ICR, DOE and EPRI have already collected data for some of the defined combinations of scrubber, coal type, and ESP control; those plants that have been identified allowed for some reduction in the number of facilities selected for testing. Some categories, unfortunately, only had three or fewer facilities (some with multiple generating units); thus, those categories required no selection, since the facilities would automatically have to test at one of the generating units falling within said category. For those categories that did have four or more facilities (some with multiple generating units) and fewer than three facilities tested by DOE/EPRI, a random starting point was selected on the "10,000 Random Digits" table and the appropriate number of facilities were chosen. Any facility with more than one generating unit within a single category was only selected once. Although each generating unit was listed, once a unit from a facility was selected the other units were eliminated from possible selection, which will allow any facility with multiple generating units having the same controls to chose the unit for speciated mercury emissions testing to be conducted. Excerpts from the randomly selected points of the table used for selection appear below. Categories within which there was no option for selection (as noted above) or within which three DOE/EPRI tests are available are not shown.

Excerpts of Columns from "10,000 Random Digits" Table Used for Selection

Category 3 picks

Population: 31

No DOE/EPRI tests	Category 9 picks

Population: 10

No DOE/EPRI tests	Category 10 picks

Population: 421

1 DOE/EPRI test
49300	34208	93734
19570	05059	78046
25411	13856
78343	18096	60629
97055	07561	40534
91910
99429	14035
68632	19174
30691
13019	12493
24357	40353
02980
40449	23310
28819	73857
43359
59788
33719

Category 11 picks

Population: 67

No DOE/EPRI tests	Category 12 picks

Population: 31

No DOE/EPRI tests	Category 16 picks

Population: 123

No DOE/EPRI tests
25984	79871	60298	96344	44412
86666	25954	36755	65994	03139
69003	27861	32769	63159	50804
65511	40846	35903	31928	87846
91305	37992	41369	44381	19091
92104	52447	55985	89928	55986
30622	49840	95090	75115	87003
17672	33054	28539	31727	07650
73437	06726
34858	71637
38112	54985
78935	32860
52000	98208
93954	33811
98102	25472

Category 17 picks

Population: 26

1 DOE/EPRI test	Category 19 pick

Population: 90

2 DOE/ERPI tests	Category 20 picks

Population: 7

No DOE/EPRI tests
85718	26619	81791
86072	23947
69722	93215
03056	62423
80747	18030
71887	39205
14515

Category 21 picks

Population: 12

No DOE/EPRI tests	Category 22 pick

Population: 12

2 DOE/EPRI tests
03494	25962
78527	44865
64525	04027
57161
53317
51423
79542
98492
85403
13045
37329
11729
95121
25669
53229
09666
92564
55448
45938
65911
33067
03542
53688
05511

Category 25 picks

Population: 14

No DOE/EPRI tests	Category 26 picks

Population: 11

No DOE/EPRI tests	Category 27 picks

Population: 21

1 DOE/EPRI test
07639	14079	07048	63759	54137
14132	25812	09165	33214	88978
15271	68348	35654	14340	12963
21199	53819	79065	91608	85910
22545	96814	27969	74473	78164
76872	45392	47528	54499	40825
80308	48300	65694	13171	86501
43715	99065	24253	33063	29924
28430	47445	34302	54969	48620
30662	38807	76809	17294	47262
47404	82043	85183	83791	01365
64876	74721	27541	39443	22352
73852	09566	74188	77782	52187
89204	13270	25078	80878
96505	89150	64031	19529
54176	49980	80642	70654
37176	26810	27186	45039
98866	35056	74012	51651
14199	09873	04301	73169
23850	40806	78215
61236	21845	48988
97384	44709	82103
82734	88151	02798
73954	66501
18548	45920

Category 30 picks

Population: 32

No DOE/EPRI tests	Category 48 picks

Population: 103

No DOE/EPRI tests	Category 49 picks

Population: 5

No DOE/EPRI tests
86360	39653	30644
47019	39769	09922
00269	09586	76595
16367	59122	78043
53815	44823	45007
27311	16926	91994
30397	93522	13012
70573	64066
11001	55973
58290	29978
20684
26414
70423
09448
05287
86462
24948
36298
76781
80681
65947
26153
51882
86747
06480