Statisticians don't often make the news. But William “Bill” Sanders became known among local teachers when the Houston Independent School District decided this month to evaluate — and possibly fire — them based on his statistical analysis of student test scores. HISD has paid Sanders' employer, the SAS Institute in Cary, N.C., more than $1.3 million since 2008 for his analysis, which is the basis of the district's performance bonus system.
Q: Teachers have criticized your formula as being too complicated. In simple terms, can you explain how you calculate a teacher's effectiveness?
A: I can't explain how you calculate it. I can explain the concept. The concept is very simple. You look at the progress rates for the individual student. The way to visualize it is, every student has his own trajectory. If the kid is having a really good year, there will be a positive bubble. If the kid is not having a good year, there will be a negative dent. By mathematically aggregating the dimples and bubbles across all students, that gives you a basis for measuring the effectiveness of the schooling entity — the district, the building or the classroom.
Q: I've heard your formula is a secret or proprietary.
A: That's not true. Sanders has given the Chronicle a paper about the Tennessee Value-Added Assessment System, which he