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DATA>
different values). Sample 'effort' was chosen as a generic term to represent very different measures
of sampling intensity which determine the amount of area searched for the various types of distance
sampling.
For point transects, the basic unit of sample effort is 1 for each time a complete point or
web is sampled. If some constant fraction, c, of the complete circle is searched for all of the points,
it is easiest to set effort=1 and use the command SF=c at the OPTION> prompt, where c is the
proportion of the circle searched. However, if only some of the point transects are searched partially,
set the effort for those samples to the fraction of the circle searched. Do not set both the effort to c
and SF=c. As an example, if for 1 point transect only 1/2 the circle was searched once and the
remaining points were completely searched once, let SF remain at its default value of 1 and enter
the effort for each sample as follows:
DATA;
SAMPLE/EFFORT=0.5;
...
SAMPLE/EFFORT=1;
...
SAMPLE/EFFORT=1;
...
{etc}
If a series of point transects are surveyed along a line and the distance between the points is small
relative to the size of the area, it is more reasonable to consider the line of points as a replicate
rather than the point. In this case, each line would be represented as a sample and the effort would
be the number of point transects along the line (if c=1 for each point) or the sum of the fraction of
the circle observed at each point (if c < 1 for one or more points).
For line transect sampling, effort is the length of a line (li) for each time it is sampled. As
with point transects, if only 1 side of the line transect is searched, sampling effort can be adjusted
for a few lines by halving the line length or it can be adjusted for all lines by setting the value of
SF=0.5; at the OPTIONS> prompt to adjust all of the lines. A partial example is illustrated below,
with the first 3 lines each sampled a single time and the lengths are 10.5,12.1 and 1.5 miles
respectively.
OPTIONS:
LENGTH/UNITS='Miles';
END:
DATA;
SAMPLE/EFFORT=10.5;
...
SAMPLE/EFFORT=12.1;
...
SAMPLE/EFFORT=1.5;
...
{etc}
For cue counting, the sampling effort is the time spent searching. The discussion above
also applies to cue counting.
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