| Characteristic | Net units in millions |
|---|---|
| - | - |
| - | - |
| - | - |
| - | - |
| - | - |
| - | - |
| - | - |
| - | - |
| - | - |
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Source
Release date
August 2017
Region
United States
Survey time period
2008 to 2016
Supplementary notes
Figures for the period 2008 to 2011 come from earlier articles.
Figures have been rounded.
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