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Federal Register / Vol. 86, No. 143 / Thursday, July 29, 2021 / Notices D. Sample Size Calculation and Allocation and Sample Selection The Bureau proposes to decide the number of grid cells that the provider has to test that is, the sample size, n, based on a set of statistical and logistical assumptions. The statistical assumption
is that the variance of the desired estimate of average population served cannot exceed a specified value, V. The logistical assumption is that the cost of drive testing is constant in every grid cell selected in the sample. Under these assumptions, a theoretical value for the

Number of grid cells in the stratum

Weight of the stratum

Mean of X in the stratum
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sample size can be calculated as detailed below.
Let L denote the number of strata in the frame and let the index h distinguish these L strata. Further, denote or define the following quantities:

= Nh thus, N = Lt=i Nh
= Wh = NhfN
= xh =

:h rf:!11

xh,i where xh,i is the value of committed population
X in the ith grid cell of stratum h
Under our proposal, the theoretical minimum sample size is given by:

Once determined, n would be allocated among the different strata. Specifically, if nh is the number of sample grid cells allocated to the stratum, then:

Guided by the allocation scheme from the previous section, staff proposes to use geographic information systems GIS tools to randomly select grid cells in each stratum, including options within these tools that ensure geographic dispersion for selected grid cells within a stratum. The provider subject to testing would then be notified of the sample grid cells in which it would be required to conduct on-theground speed tests.

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E. Drive Testing Data Collection We propose that, within each selected grid cell, a carrier would conduct a minimum of 20 tests, no less than 50%
of which are to be conducted while inmotion from a vehicle. This is the minimum number of tests to support the use of the binomial distribution to approximate the normal distribution that is needed in calculating the gap in coverage based on a one-sided 90%
confidence interval, as discussed later in Section VII.

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To be considered valid, each test should be conducted between the hours of 6:00 a.m. and 10 p.m., within the selected grid cell, and report all relevant parameters defined in Appendix A.
Each component of a test i.e., download and upload speeds should have a duration between 5 and 30 seconds.
Mobile tests are considered to be located within the grid cell containing the starting location, as a tester has full control over the starting location of a test but may not always be able to control the ending location of a test.

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This method of apportioning the sample among the various strata is called Neyman allocation.