Lies, damn lies, statistics | Arkansas Blog

Wednesday, September 1, 2010

Lies, damn lies, statistics

Posted By on Wed, Sep 1, 2010 at 6:31 AM

So-called value added evaluations of teachers are the flavor of the day. Test scores can provide an absolute measure of the effectiveness of teachers, the supporters say. You just measure the progress of each student during a year, crunch numbers and, presto, sheep and goats are separated.

The New York Times examines the topic today and points out what many have long said — the measurements can be unreliable. Naturally the inventor of the method in Tennessee says not. The minute you read, however, that some "assumptions" are made in calculating the numbers, you know, at a minimum, that there's room for subjectivity and misinterpretation.

No doubt, such a rating system has some value.

But when the method is used to evaluate individual teachers, many factors can lead to inaccuracies. Different people crunching the numbers can get different results, said Douglas N. Harris, an education professor at the University of Wisconsin, Madison. For example, two analysts might rank teachers in a district differently if one analyst took into account certain student characteristics, like which students were eligible for free lunch, and the other did not.

Millions of students change classes or schools each year, so teachers can be evaluated on the performance of students they have taught only briefly, after students’ records were linked to them in the fall.

In many schools, students receive instruction from multiple teachers, or from after-school tutors, making it difficult to attribute learning gains to a specific instructor. Another problem is known as the ceiling effect. Advanced students can score so highly one year that standardized state tests are not sensitive enough to measure their learning gains a year later.

It's the old story. People want to make things simple, to reduce even the most complex of challenges to a binary option — yes/no, good/bad, up/down. If only it were so simple. The DOG today editorializes for moving ahead with this value-added testing and spreading every teacher's score on the public record (a personnel record examination not required of any other public employee, from cop to janitor.) Consider when evaluating that idea the example of the teacher of high-achieving students in Houston who doesn't qualify for value-added bonuses because it's hard to move A students much during the course of the year. Her students start at A and end at A. Has this teacher failed? The value-added system says she has.

Tags:


Favorite

Comments (47)

Showing 1-47 of 47

Add a comment

 
Subscribe to this thread:
Showing 1-47 of 47

Add a comment

More by Max Brantley

  • Saturday's open line, plus some political notes

    The Saturday open line, with some political odds and ends:
    • Dec 15, 2018
  • Obamacare's ruin: Where are the boastful press releases from Arkansas Republicans?

    Silence so far from Republican politicians such as Leslie Rutledge on achievement of their long-stated dream, death to the Affordable Care Act. Could that be because most people now understand what a good thing President Obama did with its passage? Update: Rutledge applauds and offers empty promise of coverage.
    • Dec 15, 2018
  • Entergy demolishes old power plant near Stamps

    Entergy, the state's largest electric utility, yesterday used explosives to destroy the major parts of its closed Couch Plant near Stamps, which dated to 1943 and was designed to burn fuel oil or gas at two generating units. Named for power company founder Harvey Couch, it's been out of commission since 2013.
    • Dec 15, 2018
  • More »

Readers also liked…

  • Among the last words from Kenneth Williams: 'Finger Lickin' Good Fried Chicken'

    What's purported to be a final-words essay from condemned prisoner Kenneth Williams was distributed today by Deborah Robinson, a freelance journalist in Arkansas.  He reflects on his execution, his victims, reactions of inmates and big servings of fried chicken, which he says are given to all inmates on execution days.
    • Apr 27, 2017
  • ADEQ denies C&H Hog Farm permit

    The Arkansas Department of Environmental Quality has denied a new permit for the C&H Hog Farms' concentrated animal feeding operation near Mount Judea (Newton County). This is a big and somewhat surprising victory for critics who have viewed C&H's large-scale pig farm and the pig waste it generates as an existential threat to the Buffalo National River.
    • Jan 10, 2018
  • Presidential thriller, co-author Bill Clinton, coming to bookstores in 2018

    June 2018 is the expected publication date for a novel collaboration by former President Bill Clinton and crime writer James Patterson.
    • May 9, 2017

Slideshows

  • Arkansas vs Ole Miss at War Memorial stadium in Little Rock, Saturday, Oct. 13, 2018. After leading for much of the game, Arkansas lost 37-33 when Ole Miss scored the game winning Touchdown with less that 2 minutes left. 
  • Margaret Clark Adventure Park
    New sculptures, preschoolers play area dedicated in Riverfront Park in Little Rock.

Most Recent Comments

 

© 2018 Arkansas Times | 201 East Markham, Suite 200, Little Rock, AR 72201
Powered by Foundation