Data Viz Done Right

March 9, 2011

Facts are friendly. Why the Cobb County School Board should reinstate the balanced calendar.


Today I presented the information below at the monthly Cobb County School Board meeting.  As some background, the previous board approved a three-year “balanced” calendar that provides more frequent breaks throughout the year.  However, a new board was “elected” (some ran unopposed) and they decided that, despite the overwhelming evidence in support of the balanced calendar, they wanted to go back to the “traditional” calendar.

Naturally, I used Tableau to analyze the data that was provided by the county itself (some board members were using their own data which could neither be validated nor would they share).  The key points:

  1. The Balanced Calendar has resulted in a 26% reduction in teacher absences for a total savings of $987K. Previously when this data has been presented, it has not factored in the additional savings that result from a $10 decrease in daily substitute pay.
  2. The Balanced Calendar has resulted in a 4.2% reduction of student absences, with over 75% of school reporting a reduction in absences.  In the past, analysis has not considered that there were 88 schools days in 2010 compared to 85 in 2011.  Another interesting fact is that a school board member reported incorrect information.  I corrected him.
  3. Utility cost trends are in alignment with my costs at home.  My assumption, though likely too broad, is that my utility costs are in alignment with other residents of Cobb county.

The board is supposed to vote on the calendar again today or tomorrow, but I’m not holding out hope that the board members that voted against the balanced calendar will be swayed by facts.

I closed my comments with the following from Seth Godin:

Before we invest a lot of time in evidence-based discussions, please tell us what evidence you would need to see in order to change your mind. If the honest answer is, "well, actually, there's nothing you could show me that would change my mind," you've just saved everyone a lot of time. Please don't bother having fact-less discussions.


  1. Payrate for Substitutes for CCSD for 2010-2011 is $69.00 per day. Argument for savings due to calendar change should not include reduction in substitute pay. (Which was not $84 last school year.) Amount should be based on less days (8741) multiplied by $69.00 = $603,129.

  2. Let us know the outcome. That quote from Godin is excellent. I should remember it before I embark on some of the projects I take on!

  3. @IPjoseph: I calculated the teacher absence savings based on the rates I received from the CFO's office. I also used the total loaded cost for 2010 because that was the way it was presented to me by one of the four board members that opposed the balance calendar. I was directly addressing their incorrect numbers by stating the pay rates I used.

    The same goes for the student attendance rates. I normalized those to account for the same number of days so that my numbers aligned with what I received via an email (and that board member apparently can't count).

    @Andy: I ran across that Godin quote as I was preparing for the meeting; I don't see that as a coincidence. In the end, the board ignored the facts (and their lack thereof) and the apparent public sentiment and decided to prevent the topic from coming onto the agenda again indefinitely.

    Here's a news video from the meeting (I'm the first speaker they show). The absolutely butchered my last name. The worst misspelling I've ever seen :-)