Could someone please tell me the definition of a severe learning disability - how does it differ from learning disability? Thanks.
severe, disability, etc. (long and mathematical)
Hopefully you are familiar with the normal distribution and the bell curve. If not, these are important concepts in defining exceptionality and ranges, and you should get a nice person who knows some basic statistics to help you out. Lots of pictures! Sorry I can’t sketch any here.
Just about everything to do with humans follows a random distibution and a bell curve — height, shoe size, almost any test score, running speed, far/near-sightedness, hearing, and on and on.
In just about anything measured, there is a bunching at the center, with about 68% of the population being within one standard deviation of the mean (average). This is considered average/normal etc.
Take for example men’s height in the US (hopefully a non-controversial topic). The mean or average is around 5’9” and the standard deviation is around 2.5” (very rough numbers here, just to give an idea) So about 68% of men are between 5’6.5” and 5’11.5” and men in this group are considered average.
Another 15% or so are between one and two standard deviations above average, and the same below. These are considered “above average” or “below average” but still well within the normal ranges.
In the height example. around 15% of men are below average height, between about 5’4” and 5’6.5”, and another 16% or so are above average, between about 5’11.5” and 6’2”
The extremes start with those more than two standard deviations above or below the mean (average). About 2% of the population is in each category, exceptionally high and exceptionally low. (Because I’m rounding here we’re up to 102% — take these as rough numbers)
In the height example, about 2% of men are extremely short, between 5’1.5” and 5’4”, and about 2% of men are extremely tall, between 6’2” and 6’4.5”.
Finally the outliers are more than three standard deviations above or below the mean. Less than a tenth of one percent, or fewer than one in a thousand, are in these ranges.
In the height example, fewer than 0.1% of men are below 5’1.5” and fewer than 0.1% are above 6’4.5”
Yes, this does include nearly the entire NBA, but let’s face it, your chances of getting into the NBA are closer to one in a million than one in a thousand, so yes, these are very rare heights.
OK, now how this applies:
First of all, a couple of points of logic that escape many school administrators:
—if forty or fifty percent of your population fits into any category, that category is no longer exceptional, it has become the norm for your community. So if fifty percent of your students can’t read/do arithmetic/write legibly, unless there has been massive lead contamination in the town’s water or some other major disaster, you cannot blame the students any more, you must look at what the schools are doing.
— the Lake Wobegon effect — a town where all of the students are above average — is impossible. By the definition of a mean or average, in a reasonably large random sample, half will be above average and half will be below. Having someone below average, or being below average, is perfectly OK — if the average is reasonably close to national norms or averages. You worry when you or your child go far below average, or when your local average is far below the national.
OK, now each state and each group defines exceptional a little differently. Some take the bottom two percent, below the second standard deviation. Some take the bottom five percent, including the lower part of the low average group. Some take the bottom ten percent, including the lower half of the low average group.
Now, there are variations between people who are labelled exceptional. Taking an IQ test with a mean of 100 and a standard deviation of 16, two sd’s below average is 68. About 2% of the population will be below 68 and are considered to have definite learning weaknesses. If your state takes the bottom 5% for special ed, then kids placed in special ed will have IQ’s of about 80 or below. All other things being equal, there is a difference between the kid with a score of 79 at the fifth percentile, the kid with a score of 67 at the second percentile, and the kid with a score of 51 in the first percentile. They would have different abilities and learning needs.
A score of 51, in the lowest 0.1% of the population would usually get the label “severe”. A score of 67, in the lowest 2%, might often also be considered “severe”. A score of 79, in the lowest 5%, would more likely be called “moderate” (after all, 5% means one person in twenty is scoring below this area so it is not all that rare)
Exact numbers assigned to particular descriptions and vice versa depend on politics and finances and parental pressures and many other things, which is why researchers talk in terms of standard deviations and percentiles rather than verbal labels.
If you join the readbygrade3 yahoo group there are many definitions being discussed there right now by all kinds of people who have all kinds of ideas. It might be worth reading.
Michelle AZ