March 2018 - Parks & Recreation - 55

a chance to be chosen, and the drawing
process is random. Any sample that is
not a probability sample is a convenience
sample; for example, choosing parks because some residents who live nearby
volunteer to help is a convenience sample. Note: Subjective opinions in the sampling process, if not incorporated properly, will result in convenience samples.
Third, the chosen sample should be sufficiently large to estimate the population
characteristics. Statistically, it may be reasonable to sample around 10 percent, if
the population is not too large (e.g., sample 10 parks if the city park system has 100
parks). If the population is small, a reasonable sample may be more than 20 percent
(e.g., sample four parks if a system has 20
parks). Likewise, if the population is huge,
the sampling proportion should also be
smaller (e.g., sample 50 green spaces if the
city has more than 1,000 public green spaces). A sample must have a minimum of

two but usually should have four or more
parks. If the park system is very heterogeneous, the sample size should be increased
to ensure most or every type of neighborhood will be represented.
Besides sample size, the spacing between observation needs to be considered to provide more information. An
estimated three to four hours is necessary
between consecutive measurements in the
same park, because measuring the parks
during consecutive hours may be redundant (e.g., 10 a.m. and 11 a.m. will likely not be very different compared to the
observations taken at 11 a.m. and 3 p.m.
Geographically sampled parks should
also not be close to each other, since it is
likely they serve the same populations.
Conclusion
Measuring park use is a key step toward
putting this sector of government service
provision on par with other sectors that

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are more likely to be considered essential
to the lives and well-being of residents.
With concrete numbers to support the
demand for park services and facilities,
park and rec departments can justify the
need for park staff, maintenance, and
additional parks and facilities. If equity
is a goal, the numbers can also provide
guidance on how to better develop and
implement services. For example, parks
that are not reaching women might need
some more exercise classes, or parks
not visited by seniors may need to add
benches or have their accessibility issues
addressed. Park assessment will provide
important benchmarks to guide park
planning and management strategies.
Deborah Cohen, MD, MPH, is a Senior Scientist
at the RAND Corporation and the Principal
Investigator of the National Study of
Neighborhood Parks (dcohen@rand.org). Bing
Han, Ph.D., is Senior Statistician for RAND
Corporation (bhan@rand.org).

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Parks & Recreation

March 2018 - Parks & Recreation

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