FOR NJOSH ONLY
The Importance of Statistics, Amanda Morin
Statistics is the science of using math to make sense of and interpret large amounts of information. Statistics help evaluators:
Organize and present data in ways that are easier to understand. The information can be used to make graphs and charts that show patterns.
Describe data in ways that help you see how your child fits into a larger group of people.
Draw conclusions from data to get an idea of how best to support your child.
Testing Terms to Know
Several different terms are used to talk about test results. Knowing what these terms mean is a good start to understanding what your child needs.
1. Norm-referenced: A norm-referenced test compares your child’s scores to the scores of other kids the same age. The “norm group” is a large, random group of kids who have taken the same test.
Their scores are used to determine what’s typical for the age group. For example, on one test, the Wechsler Intelligence Scale for Children (WISC), the average score is 100.
2. Test reliability: A reliable test is one that would provide the same results every time. That means if your child took the test a few times, the scores would be roughly the same. Longer tests tend to be more reliable than short ones.
For example, the score on a test with fewer questions is more likely to be affected by your child not paying attention to one of the questions. That’s because each question is worth more on a shorter test.
If your child missed one answer on a spelling test of five words, his grade would be 80 percent. If he missed one word out of twenty, his grade would be 95 percent.
3. Standard score: Most educational tests have standard scores based on a scale that makes the average score 100. But the average always falls within a range. There’s wiggle room (sometimes referred to as “standard error”) in test scores to account for possible mistakes.
So, an average score is actually a range of numbers. For example, if an average score is 100 and the standard error is 15, that means the average is really anywhere between 85 and 115.
4. Standard deviation (SD): The standard deviation is the average distance (or number of points) between all test scores and the average score. For example, the WISC has an SD of 15 points. Most kids fall between the range of 85–115 points.
One SD (15 points) from the average or standard score (100 in this case) isn’t statistically significant. “Statistically significant” means that the difference isn’t due to chance or error.
So what does this mean? If your child’s score is only one SD lower than the average, the score is still considered average. However, if your child’s score is two standard deviations (30 points) above or below the average, that’s significant.
Keep in mind that 68 percent of the population falls into the average score range between 85 and 115. Anywhere in that range is considered average, although you may see it described as “high average” or “low average.”
5. Percentile: The percentile shows the proportion of scores that were lower than your child’s score. Imagine your child is one of 100 kids being tested. If your child is at the 75th percentile, it means he scored higher than 75 of the 100 kids tested.
Subtest Scores
Many tests are made up of a number of short tests that look at different skills. Those short tests are called subtests. An achievement test may have subtests for vocabulary, working memory and visual reasoning. Each subtest has its own score.
Sometimes the scores of subtests that look at different pieces of bigger skills are combined. For example, a vocabulary subtest and a language comprehension subtest might be combined to give a “verbal ability” score.
Subtest scores are important. When there’s a big difference in the scores of different skill groups, it can show the specific area in which your child is having difficulty.
An Example of an Evaluation Result
The evaluation report will usually have a chart that shows the different types of scores. It will also include information about the reliability of the test and the standard deviations. But it may also have a written interpretation of the results.
For example: Jane obtained a standard score of 85 (-1 SD) on the WISC, which is ranked at the 16th percentile and is classified as low average. This means Jane’s score was below the average score of 100. She scored the same or higher than 16 percent of kids her age in the general population. While her score is still considered to be average, it’s at the low end of the average range.
Putting It All Together
Scores alone don’t tell you what’s going to help your child. The summary and recommendations are where all the information comes together and the evaluator tells you what it means. The summary and recommendations section helps answer these questions:
What does this mean for your child’s ability to learn?
Do these results show that your child has learning issues that require special education services?
What types of services, ways of teaching, assistive technology and other support could benefit your child? If your child is eligible for special education services, the Individual Education Program (IEP) team will consider the answers to these questions.
The more you understand the meaning of scores from educational or psychological evaluations, the better able you are to be an active team participant.
Key Takeaways
Many tests have a range of scores that are considered average.
Subtests help show the specific skills your child has trouble with.
You can use the recommendations of an evaluation report to find ways to help your child learn more successfully.
About the Author
Amanda Morin
A parent advocate and former teacher, Amanda Morin is the proud mom of kids with learning and attention issues and the author of The Everything Parent’s Guide to Special Education
