Reply to How common is a math or reading MAP score at the 99th percentile in this area?

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[quote=Anonymous][quote=Anonymous]My kids who did get in to CES and magnet middle school got 98-99th percentile scores consistently and their elementary school acted as if those scores were unusually high and certainly not the time a dozen they are made out to be here.[/quote]
The percentiles are computed by fitting the RIT score to a normal distribution ("bell curve") based on a national, weighted sample using a stratified sampling method. The population they're trying to capture are all students in the United States, which means that local deviations are possible. Compare the county's mean to the national mean.

Also, due to the [url=https://teach.mapnwea.org/impl/MAPGrowthNormativeDataOverview.pdf]nationwide decline in student achievement[/url] (as reported by standardized test scores) that occurred in the 2015-2020 time frame, the reported percentiles using the 2015 tables are likely to be an underestimate. NWEA corrected for that with a new norming sample in the 2020 tables.

According to insider information, their model's fit to a normal distribution breaks down at around the 97.5% percentile or about 1.96 SD (NWEA doesn't officially publish how well their model fits, especially at the extremes). Their model focuses more on capturing growth percentiles accurately, a decision they pay for with higher residuals.

So we can perhaps say with some confidence that only about 1 out of 40 students (nationally) scores at or above the 97.5% percentile with respect to the norming sample, but we probably cannot say the same for the 99% or 99.9% (the latter of which NWEA rightfully doesn't even include in their tables). So if your child scored 3, 4, or 5 standard deviations above the mean that doesn't mean they're one in 741, 31,574, or 3,486,914 if you cared to look up those numbers ;-)
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