Sampling and Non-Sampling Errors

The goods data are a complete enumeration of documents collected by the U.S. Customs and Border Protection and are not subject to sampling errors; but they are subject to several types of nonsampling errors. Quality assurance procedures are performed at every stage of collection, processing and tabulation; however the data are still subject to several types of nonsampling errors. The most significant of these include reporting errors, undocumented shipments, timeliness, data capture errors, and errors in the estimation of low-valued transactions:

Reporting Errors: Reporting errors are mistakes or omissions made by importers, exporters or their agents in their import or export declarations. Most errors involve missing or invalid commodity classification codes and missing or incorrect quantities or shipping weights. They have a negligible effect on import, export and balance of trade statistics. However, they can affect the detailed commodity statistics.

Undocumented Shipments: Federal regulations require importers, exporters or their agents to report all merchandise shipments above established exemption levels. The U. S. Census Bureau has determined that not all required documents are filed, particularly for exports.

Timeliness and Data Capture Errors: The U.S. Census Bureau captures import and export information from administrative documents and through various automated collection programs. Documents may be lost, data may be incorrectly keyed, coded or recorded. Transactions may be included in a subsequent month's statistics if received late.

Low-Value Shipments: The total values of transactions valued as much as or below $2,500 for exports and $2,000 ($250 for certain quota items) for imports are estimated for each country, using factors based on the ratios of low-valued shipments to individual country totals for past periods.

The U. S. Census Bureau recommends that data users incorporate this information into their analyses, as nonsampling errors could impact the conclusion drawn from the results. For a detailed discussion of errors affecting the goods data, see "U.S. Merchandise Trade Statistics: A Quality Profile."

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