NORMDIST gives thearea under the normal curve(with mean and vari-
ance provided) all the way from the far-left side (minus infinity) to the
valuex that you have to specify. For example, if you specifym¼0 and
s¼1, the return is the area under the standard normal curve up to the
point specified (which is the same as the number from Appendix Bplus
0.5).
NORMINV performs the inverse process, whereyouprovide the area
under the normal curve (a number between 0 and 1), together with the
meanmand standard deviations, and requests the pointxon the hori-
zontal axis so that the area under that normal curve from the far-left side
(minus infinity) to the valuexis equal to the number provided between 0
and 1. For example, if you put inm¼0,s¼1, and probability¼ 0 :975,
the return is 1.96; unlike Appendix B, if you want a number in the right
tail of the curve, the input probability should be a number greater than 0.5.The t Curves: Procedures TDIST and TINV We want to learn how to find the
areas under the normal curves so that we can determine thep valuesfor statis-
tical tests (a topic starting in Chapter 5). Another popular family in this cate-
gory is thet distributions, which begin with the same first two steps: (1) click the
paste function icon, f*, and (2) clickStatistical. Among the functions available,
two related to thet distributionsare TDIST and TINV. Similar to the case of
NORMDIST and NORMINV, TDIST gives thearea under the t curve, and
TINV performs the inverse process where you provide the area under the curve
and request pointxon the horizontal axis. In each case you have to provide the
degrees of freedom. In addition, in the last row, marked withtails, enter:
(Tails¼) 1 if you wantone-sided
(Tails¼) 2 if you wanttwo-sided(More details on the concepts of one- and two-sided areas are given in Chapter
5.) For example:
Example 1:If you enter (x¼)2.73, (deg freedom¼) 18 , and, (Tails¼) 1 ,
you’re requesting the area under atcurve with 18 degrees of freedom and
to the rightof 2.73 (i.e., right tail); the answer is 0.00687.
Example 2:If you enter (x¼)2.73, (deg freedom¼) 18 , and (Tails¼) 2 ,
you’re requesting the area under atcurve with 18 degrees of freedom and
to the rightof 2.73 andto the leftof2.73 (i.e., both right and left tails);
the answer is 0.01374, which is twice the previous answer of 0.00687.EXERCISES
3.1 Although cervical cancer is not a leading cause of death among women
in the United States, it has been suggested that virtually all such deathsEXERCISES 141