MINI CASE 11.1
We have said that things which are affected by numerous factors often have a Normal distribution and one example of this is a person's IQ score. As testing developed it was often for specific age groups but most testing is currently done on adults and a comparison is made to historical scores by people of the same age. The mean is set at 100. The Internet site www.iqtest.com shows the following table:
And from this we can see that the standard deviation must be 15 since we know that 68 per cent of a Normal distribution is within one standard deviation of the mean, and the range given in the table is from 85 to 114. Looking at the table you can see how the Normal distribution shows the percentages in each group. If in doubt, convert the scores to Z-scores and look up the values in Appendix C.
Source: www.IQtest.com (accessed 29 December 2011)
Reproduced by permission of IQTest.com