Scott Wedel: School demographic projections still in question
November 13, 2018
I read the newspaper article on the Steamboat Springs School District community forums seeking input on proposals to solve overcrowding and am stunned the normal process has again been short-circuited.
The school district predicts 3,000 students by 2030. The source of those numbers is district staff performing a straight line projection assuming that current enrollment will grow at a steady rate for the next 11 years.
I have a hobbyist’s interest in demographics. About the first thing a person learns when studying demographics is straight line projections are prone to being extremely inaccurate. The size of next year’s kindergarten class is not affected by the size of this year’s kindergarten class. Thus, straight line projections using a previous year’s kindergarten class to predict the size of future kindergarten classes is awful demographic methodology.
Using a straight line projection on district enrollment creates a model of every grade remaining in the same grade, not a single student advancing, for the next 11 years while the class sizes get larger as more people move in. It is an absurd model.
It is similar to the bad model used to justify the Overlook high school proposal in 2015, which also used a straight line projection. That 2015 model predicted that fall 2018 would have 223 kindergarten students in Steamboat school district. Actual fall 2018 kindergarten enrollment is 138. That is a big prediction error over just three years. That is the sort of difference between projecting that we desperately need new schools while actual K-5 enrollment has declined since 2015.
The proper methodology is to create cohorts by grouping people by age. For school enrollment, that is grouping students by grade so next year each cohort advances to their next grade and births five years ago form the the current kindergarten class.
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Simple fact is that past seven years have had 945 births to parents living within the school district while previous seven years had 1,104. A cohort analysis allowing for 3 percent annual net influx shows K-5 enrollment decreasing by 160 students over the next five years to well below the capacity of the district’s current elementary schools.
Simply put, small birth cohorts since 2016 have been and will continue to replace larger cohorts in the schools.
I don’t understand why we are rushing to considering building configurations prior to getting professional demographics analysis on likely future enrollment especially when we have declining K-5 enrollment that is very likely to continue for the next five years.