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need help about this one - dreamlot
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10-22-2007, 07:39 PM
THE WAIS-R is standard IQ test witha mean 100 and SD of 15. a person with IQ 115 is at what percentile of IQ?
A. 50th B.68th C.84th D. 95th my answer is 68th, but the answer is 84th, I really need help?
10-22-2007, 07:48 PM
SO HERE ITS MEAN PLUS/MINUS 1XSD WHICH COMES TO 115 AND 85 RANGE.
SO IT HAS TO BE 68 BUT SINCE 115 IS ON THE EDGE OF THE RANGE IT COULD BE 84TH, HOWEVER AM NOT TOO SURE BOUT THAT
10-22-2007, 07:58 PM
this one is really tricky. imagine a normal curve, 68% is the area between -1SD and +1SD. so if it is divided by 2, you get 34% for an area of one side. the percentile is calculated by: 50% (all the left side area) plus 34% (right side area of 1 SD). therefore, the answer is 84%. hope i make you understand, very tricky. I might easily make the same mistake as yours on test day.
10-22-2007, 08:27 PM
ok, the 115 is above +1SD, so, it should be 34%, but why add 50%?
10-23-2007, 04:10 AM
the half of the curve means 50.....the curve is a measure of NORMAL DISTRIBUTION
that means 50% of the population are from the middle to the left and 50% are from the middle to the right If a person is 1 DS high, means that is not in hte middle........ is moving to the right. How much to the right? Well 50 if were in the middle........plus 34 if 1 DS plus 47.5% ( 34 + 13.5) if 2 DS |
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