As with many other OECD countries, the United States of America (U.S.) estimated the literacy skills of its adult population as part of the International Adult Literacy Survey (IALS). The U.S. published the results of its National Adult Literacy Survey (NALS), which employed what became the English version of the IALS test (National Center for Education Statistics 1993), and then published the results of a second estimate in 2006 after the completion of the National Assessment of Adult Literacy (NAAL), which employed a new version of the same test. The NAAL (National Center for Education Statistics, 2006) changed the familiar five levels of skill identified in the IALS to four levels, labelled: below basic, basic, intermediate, and proficient. In addition, it eliminated several million adults from the sample who were unable to answer any of the test questions. The score range in the below basic level is slightly beneath that of IALS Level 1, while the score range in basic is slightly below that of IALS Level 2. Though the actual reporting of NAAL levels is different, any particular score on the NAAL is considered equivalent to that score on the IALS and NALS.