# Baseline

**URL:** <https://forum.certara.com/t/baseline/3522>\
**Category:** Phoenix WNL basics\
**Created:** [December 10, 2020, 11:05pm UTC](https://forum.certara.com/t/baseline/3522 "2020-12-10T23:05:03Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![luoxia](https://avatars.discourse-cdn.com/v4/letter/l/b487fb/32.png) [@luoxia](https://forum.certara.com/u/luoxia)\
**Post date:** [December 10, 2020, 11:05pm UTC](https://forum.certara.com/t/baseline/3522/1 "2020-12-10T23:05:03Z")

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To calculated changes, the transformation function of baseline can help. However, not flexible enough. Is there a way to flag first or last observations within a group which is sorted by some variables. for example, find the baseline as last valid value before dosing, it could be in screening or predose on Day 1.

Lisa