Concept explainers
Transepidermal water loss (TEWL) is a measure of the rate that water crosses the skin through diffusion and evaporation. In general, damaged skin has a higher TEWL than nondamaged skin. A report submitted to the U.S. Food and Drug Administration (Therapeutic Equivalence of Topical Products, A. Bunge, B. N’Dri-Stempfer, et al., 2007) described an experiment in which the outer layer of skin on a small area of the forearm was partially removed in order to measure the concentration of a certain drug. TEWL (in g/m2 per hour) was measured both before and after skin removal. The results for 10 individuals were as follows.
Subject | Before | After |
1 | 18 | 27 |
2 | 12 | 19 |
3 | 14 | 19 |
4 | 11 | 20 |
5 | 12 | 22 |
6 | 17 | 26 |
7 | 16 | 18 |
8 | 18 | 26 |
9 | 14 | 22 |
10 | 14 | 24 |
Find a 98% confidence for the increase in TEWL.
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