PharmaSUG 2012 - Paper PO02 Does NODUPKEY Select the First Record in a By Group?

Does the NODUPKEY option in the SORT procedure always select the first observation in a group of variables? There are some who say it does and some that say it does not. This paper looks into this question, with examples, and shows that the NODUPKEY has really no effect on whether the first observation in a group of data gets selected, but does find that there are two other options that effect whether this happens and presents the effects of these options. Because these two options are rarely specified in programming and the default values shipped with SAS are almost always used, if these values are changed, unexpected results will happen.