none have evaluated
Since "none" is referring to plural "previous studies" shouldn't it take a plural verb (have evaluated)
11-13 Previous studies have shown a change in blood count parameters in persons living above sea level, but none have evaluated the effect of living below sea level.
That's right – none can be singular or plural depending on what it is referring to. To add to Tolley's suggestion, you could also write:
. . . but none of these studies have/has (whichever you feel more comfortable with – both are correct) evaluated the effect of living below sea level.
There are a couple more issues to address, however. If 11-13 is some kind of section heading (I'm wondering about this because you have a capitalized Previous) then you should separate it with a period. If you are saying, Between 11 and 13 previous studies . . ., you should phrase it as I have done to avoid beginning the sentence with numerals. The alternative would be to spell out Eleven to thirteen previous studies . . . (note lower-case p).
Additionally, you need a hyphen in blood-count (this is an open compound noun functioning as an adjective) so as to avoid any possible ambiguity between parameters of the blood count (your meaning) and count parameters of the blood (no such thing). In other words, the blood does not have count parameters, whereas the blood count does.
|link comment||edited Oct 02 '12 at 18:52 Peter Guess Expert|
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