Mueller, Julie M. (2012) Fact sheet: Estimating Flagstaff residents' willingness to pay for forest restoration in the Lake Mary and Upper Rio de Flag Watersheds: A pilot study. Other. NAU Ecological Restoration Institute.
Ng, Pin T. (2013) XLR: A free Excel add-in for introductory business statistics. Open Journal of Applied Sciences, 3 (1). pp. 32-36. ISSN 2165-3925