Geoscience Reference
In-Depth Information
Turning to recording rules, a continuous record contains the times at
which each behavior started and ended, and thereby reveals true frequencies
and durations. Instantaneous sampling characterizes the current behavior at
predefined intervals. One-zero sampling records whether a behavior happened
in one particular interval of defined length. The most common combinations
are focal sampling with a continuous record, scan sampling with an instanta-
neous record, and focal sampling with a one-zero record.
AD LIBITUM SAMPLING
An obvious bias in ad libitum sampling would arise if a researcher's presump-
tions led to particular individuals being disproportionately represented in the
sample, thereby distorting their importance. This effect has been credited with
the overestimation of male roles in the societies of some primates and may sub-
sequently have been countered by contrasting biases (Lindquist and Bernstein
1987; Morell 1993). Furthermore, individuals or behavior patterns that are
less conspicuous (because of short duration, subtlety, or association with
obscured locations) tend to be underrepresented by ad libitum sampling. For
example, Bernstein (1991) demonstrated that using ad libitum sampling of
rhesus monkeys (
Macaca mulatta
), the frequencies of contact aggression and
avoidance were underestimated whereas that of chasing was overestimated. A
related and insidious bias may affect the initial choice of study group. Sharman
and Dunbar (1982) noted that studies of baboon behavior tend to involve
larger than average groups. This erodes the generalizability of the results
because the behavior of individuals was systematically influenced by the size of
the group. In the same vein, perhaps the bias of primatologists' expectations
for their own taxon has lead to primates being described as having peculiarly
complex social lives (Rowell and Rowell 1993). However, other taxa also
emerge to have intricate societies, an obvious example being the Carnivora
(Creel and Macdonald 1996). Despite this family of biases, ad libitum sam-
pling can be useful during the naturalistic observation phase of pilot studies
and is valuable as an adjunct to more rigorous protocols that might otherwise
exclude important events that fell beyond their scope.
FOCAL SAMPLING
Because the whole attention of one observer is likely to be absorbed by one
focal subject, focal sampling risks losing valuable contextual and simultane-
ously comparable information. The temptation to follow one focal individual
