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FAQs about the New Sample Selected for the Weekly Natural Gas Storage Report

Released: August 16, 2018

Why is EIA updating the Weekly Natural Gas Storage Report (WNGSR) sample at this time?

The Weekly Natural Gas Storage Report (WNGSR) estimates of natural gas in underground storage are based on a sample survey, the EIA-912, Weekly Underground Natural Gas Storage Report. Sample reselections are necessary from time to time to capture changes in the population. The EIA-191 survey, Monthly Underground Natural Gas Storage Report, collects information from all storage operators, and it is the frame from which the WNGSR survey sample is drawn. Following standard statistical practice, EIA reselects survey samples periodically to more accurately reflect the population being surveyed.

Is EIA changing the established methodology to draw the sample or to estimate stocks and net changes?

The established methodology for drawing a new sample and estimating storage stocks and net changes has not changed. See Methodology for EIA Weekly Underground Natural Gas Storage Estimates for more information about the WNGSR sampling and estimation methodology.

When will the new 2018 sample replace the old 2015 sample?

The transition to estimates based on the new sample will occur in two steps. First, using the new sample, EIA will provide historical revisions to WNGSR estimates for the most recent eight weeks (July 13, 2018 – August 31, 2018). These revisions will be published on Monday, September 10, 2018, outside of the regular WNGSR publication schedule. Then, on Thursday, September 13, 2018, EIA will begin publishing estimates using the new sample in the WNGSR during the regular publication cycle.

How different is the sample size for the new (2018) sample compared to that for the old (2015) WNGSR sample?

The size of the new sample is very similar to the size of the old sample. The new sample includes 85 operators from a sampling frame of 134 operators in the Lower 48 states, and the old sample included 79 operators. The net effect of this sample reselection is that 17 operators are added and 11 operators are dropped. Except for the Pacific region in which a census of all eight operators will be surveyed, the operators common to both the old (2015) and new (2018) samples account for at least 93% of the total volume for the sample in each region, based on the measure of size used to select the new (2018) sample.

How different is the coverage of the new (2018) sample compared to that for the old (2015) WNGSR sample?

The coverage of the new sample is very similar to the coverage of the old sample in terms of the measure of size that was used to select the sample, which was based on monthly working gas stocks collected in EIA-191. For the Lower 48 states, operators in the new sample account for 97% of the total measure of size compared to 95% for the old sample. The coverage by region is slightly higher for the new sample. Because of the relatively small number of operators (eight) in the Pacific region, estimates of working natural gas stocks in that region will be based on weekly reports from all of them, i.e., a census data collection, for the first time. For other regions, the operators common to both the old and the new samples account for at least 93% of the measure of size used to select the new sample.

What is the difference in storage stock estimates between the new and old samples?

Since February 2018, differences in weekly estimates of working natural gas stocks between the new (2018) and old (2015) samples for the EIA-912 are not statistically significant at the 5% level of significance. Also, differences in interpolated monthly estimates derived from weekly stock estimates, compared with the monthly data based on the census survey information from the EIA-191, are similar for February 2018 through May 2018.

Will the WNGSR products, data files, or formats change when EIA begins using the new sample? Will there be opportunities to test any new products?

The WNGSR report tables, data files, and formats will not change with the new sample. Implementation of the new sample will not affect WNGSR products published on EIA’s website, including the wngsr.txt, wngsr.csv, and wngsr.json. No new weekly data files or tables will be produced. Therefore, EIA will not have a period of public testing.

What companies are currently being sampled? Can I get respondent-level data so I can build my own history?

The data submitted on the Form EIA-912 are protected under the Confidential Information Protection and Statistical Efficiency Act that precludes EIA from naming any identifiable information about the companies that report. However, monthly storage data, including operator name, location, and capacity, are available for all reporting operators in our public query system.

When will the formal changeover to the new sample occur?

The changeover to the new sample will be completed starting with the report for the week ending September 7, 2018, which will be published on September 13, 2018. On September 10, 2018, EIA will publish revised estimates for the eight-week-transition period (weeks ending July 13, 2018 to August 31, 2018) that will incorporate a blending of estimates from the old and new samples. These revised estimates will follow the procedures for reporting revisions included in the WNGSR methodology.

Will EIA issue revised estimates as a result of the sample reselection?

On September 10, 2018, EIA will publish revised estimates for the eight-week-transition period (weeks ending July 13, 2018 to August 31, 2018) that will incorporate a blending of new sample and old sample estimates. These revised estimates will follow the procedures for reporting revisions included in the WNGSR methodology.

Will other nonsampling changes to the WNGSR be implemented with the new sample?

The estimates from the 2018 sample reflect a change in data collection practices for a few operators reporting working natural gas in the South Central region on the Form EIA-912, Weekly Underground Natural Gas Storage Report. Previously, for most respondents operating both salt and nonsalt fields in the South Central region, EIA internally classified the entire inventory reported based on the field type having the preponderance of the volume. The most recent version of the Form EIA-912, approved by the U.S. Office of Management and Budget in late 2017, requires storage operators in the South Central region to separately report the volumes of working natural gas held in salt facilities and nonsalt facilities. Also, in the WNGSR, EIA will perform independent rounding for all published weekly estimates of working natural gas stocks. Currently, weekly estimates of working natural gas stocks for the Lower 48 states are derived by summing the corresponding weekly estimates by region.

Where can I find additional information about the new (2018) and old (2015) samples?

EIA provides additional information about the sample reselection for WNGSR.

For additional information contact Jose Villar at jose.villar@eia.gov or (202) 586-9613.