As Kansas students start back to high school this fall, how many of them will graduate four years from now?

According to new data released by the EPE Research Center, Kansas graduates 75.1 percent of its high school students. In a general way, we can say that three-out-of-four students who enter high school graduate with a high school diploma four years later.

But the problem is far more complex. Let us say that you think that all freshmen should graduate four years latter and nothing less than 100 percent is acceptable. Well, the chance of a freshman class being the same student population when they become the graduating senior class is not high.

Students do die in car accidents and for other reasons. Some students move out-of-district. The failure of such students to graduate with their senior class is no indication of educational quality at all. In growing school districts, an influx of high school students could result in more graduating seniors than there were entering freshmen four years earlier. Both of these problems loom large in schools serving military bases where populations move en masse.

Some students may have learning difficulties that prevent them from completing in four years. Again the graduation math is unrelated to the quality of their educational experience. But that does not prevent educationists from providing data to abuse.

The "cohort rate" is the percent of students from an entering 9th grade cohort who graduate with a standard diploma in four years and it has all the problems mentioned above.

The "composite rate" is the proportion of students estimated to remain in high school until grade 12 and receive a diploma and is calculated by multiplying the rate of persistence between grades 9 and 12 and the percent of completers who receive a diploma.

The "leaver rate" is the percent of students leaving high school with a standard diploma, expressed as a proportion of all those documented leaving.

The "national governor’s rate" measures the number of on-time graduates in a given year divided by the number of first-time entering 9th graders four years earlier adjusted for transfers.

The "NCLB rate" is the percent of students, measured from the beginning of high school, who graduate from high school with a regular diploma (not a GED or other alternative) in the standard number of years.

A "persistence rate" is the percent of students who remain in school from grade 9 through grade 12 calculated using the percent of students not dropping out or the percent of students estimated to be promoted from grade-to-grade.

Finally, the "cumulative promotion index" published in "Diploma Counts" by Education Week uses this index which computes the percent of public high school students who graduate on time with a diploma. Four steps are used: each of three grade-to-grade promotions (9-to10, 10-to-11, and 11-to-12) and those who earn a diploma. It then multiplies grade specific promotion ratios together. It is not perfect in reflecting all the non-educational factors involved in high school drop-outs. But this is the index that provides the 75.1 percent figure.

Readers who now understand the complex factors preventing a clear analysis of graduation rates, or inversely drop-out rates, will rightly be more hesitant to make quality-of-education judgements about teachers and schools. Kansas ranks 17th in the country. Many states "above" Kansas simply have fewer military bases or English-language learners or a less mobile population.

No matter which formula is used, the Kansas rate of 75.1 percent looks pretty good compared to the total U.S. rate of 68.8 percent. But compared across other developed countries? Not so good.