BMP - Tree Risk Assessment - 10

Quantitative Risk Assessment

Quantitative risk assessment estimates numeric values for the probability and
consequences of events, and then produces a numeric value for the level of
risk, typically using the formula:
Risk = Probability × Consequences
An advantage of quantitative assessment is that tree risk can be compared not only to other trees but also to other types of risk, as might be
necessary for municipal decisions in which resources must be allocated
among departments, for example. The calculations can vary from simple
to complex as risks are analyzed independently or in combination. Even
if complex statistical analyses are carried out, users must remember that
the calculations are estimates and must ensure that the accuracy and
precision reported are consistent with the data and methods employed.
In most cases, the numeric inputs required for quantitative assessments
are derived from subjective interpretations and may vary significantly
among assessors. Our ability to quantify probability is often limited
when applied to trees because they are natural structures and we have
little systematically-collected data on which to base probabilities. Since
numeric data are not always available and both systematic and statistical
uncertainties can be high, full quantitative analysis is often not warranted
or practical for tree risk assessment.

Qualitative Risk Assessment

Qualitative risk assessment is the process of using categorized ratings of
the likelihood and consequences of an event to determine a risk level and
evaluate the level of risk against qualitative criteria. Often, ratings are
combined in a matrix to categorize risk. Inherent subjectivity and ambiguity are also limitations of the qualitative approach. In order to increase
reliability and consistency of application, it is important to provide clear
explanations of the terminology and significance of the ratings defined for
likelihood, consequences, and risk. Qualitative risk assessment approaches
are recognized and respected methods of risk assessment that are used
internationally by many governments and businesses.

Qualitative Numeric Assessments

There are several qualitative numeric tree risk assessment systems that
have been used to assign numbers to certain factors to derive an estimate
or ranking of relative risk. The rankings are sometimes used to prioritize
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BMP - Tree Risk Assessment

Table of Contents for the Digital Edition of BMP - Tree Risk Assessment

Table of Contents
BMP - Tree Risk Assessment - Cover1
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BMP - Tree Risk Assessment - Table of Contents
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