Source: U.S. Department of Energy, Energy Information Administration (government).
Petroleum supply data are collected by the Petroleum Division in the Office of Oil and Gas of the Energy Information Administration (EIA), U.S. Department of Energy (DOE). The Bureau of Transportation Statistics (BTS) produced the pipeline component of the Transportation Services Index (TSI) using two data sources, from EIA, the Monthly Product Pipeline Report and the Monthly Crude Oil Report, both of which are published in DOEs Petroleum Supply Monthly.
Monthly petroleum supply data include the measurement of supply and the disposition of crude oil and petroleum products at both national and regional levels. The data series describe production, imports and exports, movements, and inventories of petroleum products in thousands of barrels. The Monthly Petroleum Supply Reporting System (MPSRS) was implemented in January 1983.
A sample is a subsection of universe-identifying members of a target population. There are five samples, one for each weekly petroleum supply survey, in the Weekly Petroleum Supply Reporting Systems (WPSRS). The weekly surveys are administered to samples of the monthly populations to reduce respondent burden and to expedite the turnaround of data from survey respondents to the public. As with any sample, the value obtained differs from that obtained if the full universe is surveyed.
Sampling error is the difference between a sample estimate and a population value. For these surveys, the EIA minimizes the sampling error by using a minimum 90% multiattribute-cutoff sample of the corresponding monthly surveys frame. At the end of each month, updates are made to the samples and survey frames if 90% coverage was not obtained.
For the weekly surveys, better coverage will likely reduce sampling error. Of the 21 products and supply type combinations, 19 had coverage of 90% or above in 2001. For 11 of the 21 combinations, 2001 coverage increased from 2000. Tabulations were done before rounding of the coverage values. Jet fuel imports display a large percentage increase from 2000 to 2001, from 64 to 91% because of the resolution of noncompliance issues.
Unlike sampling errors, all survey data, even those from a census survey, are at risk of incurring nonsampling errors. There are two categories of nonsampling errors, random and systematic. With random error, on average, and over time, values will be overestimated by the same amount they are underestimated. Therefore, over time, random errors do not bias the data, but they will likely give an inaccurate portrayal at any point in time. On the other hand, systematic error is a source of bias in the data because these patterns of errors are made repeatedly.
The list of all companies identified as members of the target population is called a frame. If members of the target population are not included in the frame, there is an undercount of the aggregate data. To diminish the chance of undercounting, the MPSRS frames are continually updated. New companies are identified through continual review of petroleum industry periodicals, newspaper articles, and correspondence from respondents.
EIAs authority to collect data comes from several laws, including the 1974 Federal Energy Administration (FEA) Act (P.L. 93-275, 15 USC 761), the 1976 Energy Conservation and Production Act (P.L. 94-385, 15 USC 790) and the1977 Department of Energy (DOE) Organization Act (P.L. 95-91, 42 USC 7135), which established EIA as the single federal government authority for energy information and gave EIA independence from the rest of DOE with respect to data collection, and from the whole government with respect to the content of EIA reports.