through 2009 are averaged. This five year average is used to account
for variations in year to year visitation due to unusually high visitation
years, weather events, etc. Only those recreation visits
occurring from May through September of each year are included in
the population estimate, as these were the months our survey was
conducted. Based on data from the National Park Service Public Use
Statistics Office, this results in an average of 2,773,685 annual
recreation visits to Yellowstone National Park. However, as
mentioned previously, an unexpectedly high percentage of survey
respondents reported seeing a bear. It is possible that sampling at
certain locations, such as road pullouts and possibly trailheads,
resulted in a sample containing a higher proportion of visitors
focused on wildlife viewing in particular than what is representative
of the overall population of summer Park visitors. Unfortunately,
there is no way to compare the proportion of visitors
sampled at each location with the actual population of users at
these locations, which is a limitation to sampling at locations
within the Park rather than at the entrance stations. So there remains
some uncertainty as to whether our sample of survey respondents
is truly representative of all Park visitors. A conservative
approach is to aggregate sample results to only that population of
Park visitors who participated in wildlife viewing specifically. A
recent survey of a random sample of summer Park visitors conducted
for Yellowstone finds that 82% of visitors participated in
wildlife viewing on their most recent trip (Kulesza et al., 2012).
Therefore, we aggregate our results to 82% of the summer recreation
visits, for a total of 2,274,422 visits.