Are the distributions of thicknesses skewed, or approximately symmetric?

Electronic devices contain electric circuits etched into wafers made of silicon.
These silicon wafers are sealed with an ultrathin layer of silicon dioxide, in a process known as oxidation. This can be done with either new or recycled wafers.
In a study described in the book Statistical Case Studies for Industrial Process Improvement by V. Czitrom and P. Spagon, both new and recycled wafers were oxidized, and the thicknesses of the layers were measured to determine whether they tended to differ between the two types of wafers. Recycled wafers are cheaper than new wafers, so the hope was that they would perform at least as well as the new wafers. Following are 36 thickness measurements (in tenths of a nanometer) for both new and recycled wafers.

Transcribed Image Text:

New 90.0 92.2 94.9 92.7 91.6 88.2 92.0 98.2 96.0 91.1 89.8 91.5 91.5 90.6 93.1 88.9 92.5 92.4 96.7 93.7 93.9 87.9 90.4 92.0 90.5 95.2 94.3 92.0 94.6 93.7 94.0 89.3 90.1 91.3 92.7 94.5 Recycled 91.8 94.5 93.9 77.3* 92.0 89.9 87.9 92.8 93.3 92.6 90.3 92.8 91.6 92.7 91.7 89.3 95.5 93.6 92.4 91.7 91.6 91.1 88.0 92.4 88.7 92.9 92.6 91.7 97.4 95.1 96.7 77.5* 91.4 90.5 95.2 93.1