©2023 International Society of Arboriculture 274 Klein et al: Evaluating the Reproducibility of Tree Risk Assessment Ratings have a valid mailing address, a randomly selected replacement also occurred. Replacements were selected on the basis of next on the list following the initial 150 participants selected from each of the 3 groups. Participants were sent survey packets with a pre- paid return envelope via the United States Postal Ser- vice. The mailings for the ISA BMP and TRAQ participants were sent on 2021 February 2. The QTRA participants in the UK and Australia were sent pack- ets between 2021 March 1 and 3. The mailer included a cover letter explaining the project, survey, tree risk assessment form, and informed consent form. Partic- ipants received a flash drive that contained 3 videos (approximately 3 to 5 minutes in length with a total length of 12:11), each highlighting all of the tree parts and defects, site conditions, and pedestrian/vehicular occupancy in relation to each of the 3 trees chosen for the study. No tree or site feature was highlighted more than another so as to not direct the assessor to place more importance on a particular feature. Addition- ally, the videos provided the location of the trees (i.e., street name, city, and state), species (i.e., tree 1—Celtis laevigata, tree 2—Quercus geminate, and tree 3— Liquidambar styraciflua), and the most recent aerial image of each tree from Google Earth with the tree and fall zone circled at scale. All videos were filmed during calm weather days on the University of Flori- da’s main campus in Gainesville, Florida, USA. In addition, assessment calculators (digital assessment form) and information sheets for each risk assess- ment method were included on each flash drive. Participant Tree Risk Assessment Participants were asked to assess each of the 3 trees using the assessment method that they were trained in (i.e., QTRA or TRAQ). The ISA BMP group was asked to use the ISA TRAQ method for tree risk assessment. For each tree, the target of concern (i.e., pedestrian or vehicle) was provided on the assess- ment form. Tree risk assessment through TRAQ had participants determine the likelihood of impact (i.e., very low, low, medium, or high), likelihood of failure within a 1-year and 3-year timeframe (i.e., improba- ble, possible, probable, or imminent), and conse- quences of failure (i.e., negligible, minor, significant, or severe) to determine the overall risk rating (i.e., low, moderate, high, or extreme) and recommend mitigation (i.e., none, monitor, advanced assessment, pruning, cabling/bracing, or removal), while QTRA users had to determine the probability of failure within a 1-year timeframe as 1 (1/1 to > 1/10), 2 (1/10 to > 1/100), 3 (1/100 to > 1/1,000), 4 (1/1,000 to > 1/10,000), 5 (1/10,000 to > 1/100,000), 6 (1/100,000 to > 1/1,000,000), or 7 (1/1,000,000 to > 1/10,000,000); part size as 1 (> 450 mm), 2 (450 to 260 mm), 3 (250 to 110 mm), or 4 (100 to 25 mm); pedestrian target as 1 (720/hour to 73/hour), 2 (72/hour to 8/hour), 3 (7/hour to 2/hour), 4 (1/hour to 3/day), 5 (2/day to 2/week), or 6 (1/week to 6/year); and vehicular target (per day) as 1 (47,000 to 4,800), 2 (4,700 to 480), 3 (470 to 48), 4 (47 to 6), 5 (5 to 1), or 6 (none), in order to deter- mine the risk of harm (i.e., broadly acceptable, toler- able, or unacceptable) and recommend mitigation (i.e., none, monitor, advanced assessment, pruning, cabling/bracing, or removal). For vehicular targets, the average speed parameter of 32 mph (50 kph) was used, as it is the closest to that of the study sites that QTRA has listed in the matrix. All of the study sites had a posted speed limit of 20 mph (32 kph). Beyond the assessments, participants were given a modified Domain-Specific Risk-Taking (DOSPERT) Scale (Blais and Weber 2006) consisting of 6 questions aimed at gauging their tolerance for risk as well as demographic information. Additionally, there was one open-ended question asking them to describe their likes and dislikes of using the risk assessment method. Follow-up emails were sent to ISA BMP and TRAQ participants on 2021 March 1 to remind them about the survey. Similarly, QTRA participants received the same email reminder on 2021 March 23. Then on 2021 April 14, a final reminder was sent to all 3 groups of participants. An additional Dropbox link to the survey documents was sent in the final reminder email. This allowed participants access to the same files they would have received by mail. To further encourage participation, the completed survey docu- ments could be returned via email. Upon completing the survey and tree risk assessments, participants were asked to return all of the documents along with their signed informed consent forms. The majority of participants (50) across the 3 groups returned their completed packets by mail, while 10 submitted their packets via email. Statistical Approach The data collected from the survey was used to help gauge each assessor’s level of risk tolerance,
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