| Country or Area | Element | Year | Unit | Value | |
|---|
| High-income economies | Value | 2019 | million No | 3.90 |
| High-income economies | Value | 2018 | million No | 3.80 |
| High-income economies | Value | 2017 | million No | 3.80 |
| High-income economies | Value | 2016 | million No | 3.70 |
| High-income economies | Value | 2015 | million No | 3.70 |
| High-income economies | Value | 2014 | million No | 3.70 |
| High-income economies | Value | 2013 | million No | 3.70 |
| High-income economies | Value | 2012 | million No | 3.60 |
| High-income economies | Value | 2011 | million No | 3.60 |
| High-income economies | Value | 2010 | million No | 3.60 |
| High-income economies | Value | 2009 | million No | 3.60 |
| High-income economies | Value | 2008 | million No | 3.60 |
| High-income economies | Value | 2007 | million No | 3.60 |
| High-income economies | Value | 2006 | million No | 3.60 |
| High-income economies | Value | 2005 | million No | 3.60 |
| High-income economies | Value | 2004 | million No | 3.60 |
| High-income economies | Value | 2003 | million No | 3.60 |
| High-income economies | Value | 2002 | million No | 3.60 |
| High-income economies | Value | 2001 | million No | 3.60 |
| High-income economies | Value | 2000 | million No | 3.60 |
| Low income economies | Value | 2019 | million No | 6.20 |
| Low income economies | Value | 2018 | million No | 6.00 |
| Low income economies | Value | 2017 | million No | 5.80 |
| Low income economies | Value | 2016 | million No | 5.60 |
| Low income economies | Value | 2015 | million No | 5.50 |
| Low income economies | Value | 2014 | million No | 5.30 |
| Low income economies | Value | 2013 | million No | 5.20 |
| Low income economies | Value | 2012 | million No | 5.00 |
| Low income economies | Value | 2011 | million No | 4.90 |
| Low income economies | Value | 2010 | million No | 4.80 |
| Low income economies | Value | 2009 | million No | 4.70 |
| Low income economies | Value | 2008 | million No | 4.70 |
| Low income economies | Value | 2007 | million No | 4.60 |
| Low income economies | Value | 2006 | million No | 4.50 |
| Low income economies | Value | 2005 | million No | 4.40 |
| Low income economies | Value | 2004 | million No | 4.40 |
| Low income economies | Value | 2003 | million No | 4.30 |
| Low income economies | Value | 2002 | million No | 4.20 |
| Low income economies | Value | 2001 | million No | 4.10 |
| Low income economies | Value | 2000 | million No | 4.00 |
| Lower-middle-income economies | Value | 2019 | million No | 32.60 |
| Lower-middle-income economies | Value | 2018 | million No | 32.10 |
| Lower-middle-income economies | Value | 2017 | million No | 31.50 |
| Lower-middle-income economies | Value | 2016 | million No | 31.00 |
| Lower-middle-income economies | Value | 2015 | million No | 30.60 |
| Lower-middle-income economies | Value | 2014 | million No | 30.20 |
| Lower-middle-income economies | Value | 2013 | million No | 29.80 |
| Lower-middle-income economies | Value | 2012 | million No | 29.40 |
| Lower-middle-income economies | Value | 2011 | million No | 29.10 |
| Lower-middle-income economies | Value | 2010 | million No | 28.70 |
