Table 1. Abbreviations, periods, definitions, and sources of nature variables used in this paper.
| Variable | Period | N | Definition | Data Source | |
| Public Lands Visitation | BLMV | 1982–2005a | 19b | (Total recreational visits to all US BLM properties)/(Total US population) | US Bureau of Land Management & http://www.census.gov/ |
| NFV | 1939–2002 | 61 | (Total recreational visits to all US National Forests)/(Total US population) | US National Forest Service & http://www.census.gov/ | |
| NPV | 1939–2005 | 67 | (Total recreational visits to all US NPS properties)/(Total US population) | http://www.census.gov/statab/www/ & http://www.census.gov/ | |
| SPV | 1950–2003 | 24 | (Total recreational visits to all US State Parks)/(Total US population) | Statistical Abstracts of the USA http://www.census.gov/statab/www/ & http://www.census.gov/ | |
| Game Licenses | Ducks | 1935–2006 | 72 | (Total no. of duck stamps issued)/(Total US population) | Ducks Unlimited & http://www.census.gov/ |
| Fishing | 1950–2005 | 53 | (Total no. of fishing licenses issued)/(Total US population) | Statistical Abstracts of the USA http://www.census.gov/statab/www/ & http://www.census.gov/ | |
| Hunting | 1950–2005 | 52 | (Total no. of hunting licenses issued)/(Total US population) | Statistical Abstracts of the USA http://www.census.gov/statab/www/ & http://www.census.gov/ | |
| Camping | Camping | 1970–2003 | 15 | (No. of people surveyed that went camping anywhere over the past year)/(Total no. of people surveyed)c | Statistical Abstracts of the USA http://www.census.gov/statab/www/ & http://www.census.gov/ |
| mmCampingNP/NF | 1988–2005 | 18 | (No. of people surveyed that went camping in National Parks or Forests over the past year)/(Total no. of people surveyed)c | Mediamark, Inc. | |
| mmCampingSP/SF | 1988–2005 | 18 | (No. of people surveyed that went camping in State parks or Forests over the past year)/(Total no. of people surveyed)c | Mediamark, Inc. | |
| Backpacking/Hiking | ATHiking | 1935–2005 | 71 | (No. of hikers completing all 3500 km of the Appalachian Trail)/(Total US population) | http://www.appalachiantrail.org/hike/thru_hike/facts.html &http://www.census.gov/ |
| Hiking | 1970–2003 | 16 | (No. of people surveyed that went hiking anywhere over the past year)/(Total no. of people surveyed)c | Statistical Abstracts of the USA http://www.census.gov/statab/www/ & http://www.census.gov/ | |
| Backpacking | 1972–2003 | 15 | (No. of people surveyed that went backpacking anywhere over the past year)/(Total no. of people surveyed)c | Statistical Abstracts of the USA http://www.census.gov/statab/www/ & http://www.census.gov/ | |
| mmBackpackingHiking | 1988–2005 | 18 | (No. of people surveyed that went backpacking or hiking anywhere over the past year)/(Total no. of people surveyed)c | Mediamark, Inc. |
a
Data exists for 1975–1981, but we were advised by BLM (T. McDonald, pers. comm.) that while 1982 and later data were based on reported use at fee sites and recreation concessions, data prior to 1982 was not and was much less reliable.
b
BLM data does not exist for the four years 1990 and 1993–1995: this is not our omission.
c
Weighted by survey firm to best estimate demographics of US population.