A report to be released today examining graduation rates across the nation again places Hawai'i's public schools in the bottom third of the country, but education officials are disputing the methodology used to calculate the data.

According to the "Diplomas Count 2008" report, only 67.4 percent of Hawai'i's class of 2005 graduated on time, but state Department of Education officials vigorously disagree with the number. They say, according to the DOE's own calculations, that 79.5 percent of students graduated that year.

"The methodology they are using is just really poor research," Glenn Hirata, administrator of the DOE's systems evaluation and reporting section, said of the Diplomas Count report. "We don't know what that number really represents," he said.

The Diplomas Count 2008 report is the most recent education policy analysis from the nonprofit Editorial Projects in Education, which publishes Education Week. The report estimates that 1.23 million students nationwide — or about 30 percent — from the class of 2008 will fail to graduate with their peers.

While Hawai'i ranked among the 15 states with the worst graduation rates in 2005, it is just slightly below the national average of 70.6 percent, according to the report.

The same analysis last year reported Hawai'i had a 64.1 percent graduation rate in 2004, which was in contrast to the 79.8 percent reported by the DOE.

Education officials say the wide discrepancies are caused by the ways the state and the report are calculating the rates.

Currently, Hawai'i uses a "cohort" method that tracks graduation rates of individual students. That means that each year, ninth-grade students entering high school are tracked through their senior year.

Only 17 states use the cohort method, because it requires complicated and systematic tracking of a student throughout their high school career. Because of Hawai'i's statewide school system and its statewide student-tracking abilities, DOE officials argue it is one of few states capable of producing a "pure" graduation rate.

"The cohort rate is considered to be the purest and most accurate way of calculation," Hirata said.

Education Week's report, however, uses a method called the "Cumulative Promotion Index," which the DOE argues is less accurate.

Nationwide education experts also criticized the report's methodology. The Economic Policy Institute issued a statement from four researchers of the nation's graduation and dropout trends. "We find the measures of graduation rates in Education Week's Diploma Counts project ... to be exceedingly inaccurate," the statement said.

Included in the report is an estimate for the rate of graduation for Hawai'i's class of 2008. Of the 16,971 Hawai'i students who entered a public high school in 2004, only 11,435 are projected to graduate this year, for a graduation rate of 67.4 percent, the report said.