Psssst... Percentiles are NOT grades!

In my opinion, percentiles are one of the most misunderstood metrics in health-related statistics. I have read dozens of online discussions that revolve around percentiles (usually related to the height and weight of a baby or toddler) and am constantly surprised by the misinformation that gets spread in these forums. For some reason, as a society, we tend to be quite "grade-obsessed". We have been trained to believe that 80%+ is the only acceptable value for our children. So if our children are not at the 80th or 90th percentile, we think that we have somehow failed... But I am here to tell you: percentiles are NOT grades! Percentiles are a measure of how a child's data sits relative to their same-age and same-sex peers:

**NOTE: Some values have been rounded up to the nearest whole number

The average range represents the bulk of the population (68% of people). It represents the range of scores from the 16th percentile, all the way up to the 84th percentile. If your child is performing in this range then congratulations! They are average! This is a GOOD thing!

Here are a few examples in the "average" range:

• 26th percentile: This is considered to be within the "average" range. 26% of scores fall below your child's score, while 74% of scores fall above it.

• 50th percentile: perfectly "average". Half of the child's peers have lower scores while half of them have higher scores.

• 80th percentile: Still average! 80% of scores fall below your child's 'score' or 'measurement' while 20% fall above it.

Here are a few examples outside of the "average" range:

• 8th percentile: This is considered to be within the "below average" range. 8% of scores fall below this score while 92% of scores fall above it.

• 88th percentile: This score is considered "above average" and is greater than 88% of the scores from same-age and same-sex peers. Only 12% of scores fall above it.

• 1st percentile: This is considered to be in the "significantly below average" range. Less than 1% of scores fall below it, while 99% of scores are greater.

As Speech-Language Pathologists, we are concerned with speech and language scores that fall within that "below average" (13.5% of people) or "significantly below average" (2% of people) range because this suggests that your child is not yet demonstrating skills that the majority or the vast majority of their peers are. This means that they may require support in their speech and/or language skills - and this is OK! When it comes to late talkers, SLPs often use the 10th percentile as a cutoff; meaning: if your child is 18 months or older and their expressive language skills are below the 10th percentile (I.e. 90% of their peers have greater expressive language skills), then they are considered late-to-talk and would benefit from support by an SLP.

Percentiles are not a report card and are not a reflection of you as a parent! The takeaway here is that percentiles allow us to determine how your child is performing relative to their peers in various speech and language skills in order to decide whether or not your child would benefit from early intervention.

-- Meg