Amateur-built and experimental aircraft - Australian Transport Safety ...

Odds ratios
An odds ratio presents the proportion of people with a variable of interest present to
those where the variable is absent. This study uses crude odds ratios to calculate the
magnitude of association. 26 For example, the proportion of people who do transition
training by those who do not do transition training for high performance aircraft.
Using the transition training and aircraft performance example, if the proportion of
people who perform transition and own a high performance aircraft is greater
among those owning lower performance aircraft, the odds ratio is greater than one.
A 50 per cent increase in the odds of performing transition training is represented as
one-point-five (1.5) and a 100 per cent increase is represented as two (2). If the
proportion of people who do transition training is equal, then the odds are one (1),
but if people who have high performance aircraft are less likely to perform
transition training, the odds are less than 1, such as zero-point-five (0.5) (Table 2).
If several categories are compared, the odds of an event can be calculated for each
category. This is usually performed by choosing a reference category, and then
comparing each category to the reference category. The choice of category in this
report is based on experience, or type of licence, given that there is a linear
relationship or a series of steps that precede the next category.
Table 2: How to interpret odds ratios
Odds ratio Interpretation Likelihood
Equal to 1 Odds are no different Same
Greater than 1 Odds are increased More likely
Less than 1 Odds are decreased Less likely
26
This is a simple proportion. An odds ratio can also be calculated using a regression equation, but
these are not used in this report.
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