Worker productivity deficit & the ADA

Factual Questions
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Inspired by this thread http://boards.straightdope.com/sdmb/showthread.php?t=294486, and not wanting to hijack it …

This situation is hypothetical, but resembles one I’ve seen and one I may run into again. Imagine I’m a US private business with a worker with a clearly recognizable handicap. As a clear result of their handicap, they can perform every function of the job, just like the person next to them, however they do it at about 1/2 the speed.

Their error rate is comparable to the others, and the speed issue doesn’t have a huge follow-on effect, i.e. it’s not a production line job where they’d be bottle-necking the whole factory. Stuff just flows from their in-basket to out-basket at half speed. Assume we’ve already applied all the assistive technology available.
How much accomodation to their performance deficit is required? None? A “reasonable” amount? If so, how much is that & how do we decide? Complete & total acceptance of any size defict no matter how large?

The non-handicapped workers in the same job vary in production speed by, say, 5-10%, maybe a little more if we factor in smoke breaks for smokers or extra potty breaks for the small-bladder crowd.

Clearly if the handicapped worker worked at 1% of the rate of the others, I’d be paying in effect 100 times as much to get the same product out the door, assuming consistent wages. I’d be accomodating this worker by accepting productivity from them I’d never accept from a non-handicapped worker.

Now what if they worked at 99% of the speed of the others? That’s probably too small a difference for me to even detect, and is certainly within the range of normal variation of workers. So my accomodation would be negligible and I expect it’d be illegal (not to mention definitely stupid & mean-spirited) to get rid of this employee based on performance.

But where in that range from 99% of normal down to 1% of normal does their performance degrade to the point that we can say they can’t perform an essential job function, or the entire job? Or is this not an ADA issue at all and I’m free to hold them to the same productivity standards as any other worker?
In addition to expert opinions I’d like any references to websites with useful tidbits. I’ve tried searching and there’s lots of info on the duty to make assistive changes in duties or equipment or facilities (the whole “reasonable accomodation” schtick), but I’ve found no mention of reasonable accomodation in terms of performance / productivity.

Thanks in advance.

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If getting the product out is an essential (as opposed to marginal) function of their job, I’d say that you have a right to prorate their salary based on performance, especially if there are other workers performing the same job at a higher rate of productivity.
To this end, there is something called Supported Employment, where an individual with a disability who performs at less than a standard rate of productivity will make less than a competetive wage, but they are able to hold the job and have accomodations. This link expalins supported employment models, although it states that the employee receives “the same wages and benefits” as non-disabled employees, and that hasn’t always been my experience.

This link might answer some of those questions.

This link provides some good information on what various states are trying to do with regards to equal opportunity and best practices.

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For the record, I answered the first part of your question based on the original example you gave—someone with an obvious disability who performs at approximately 50% the speed a non-disabled emplyee does. This doesn’t mean that I think he should only get 50% of the pay, but many Supported Employment programs do have a formula for figuring out what an employee should be paid if he or she is only doing part of the job.