Geoscience Reference
In-Depth Information
of size 3 was taken from each stratum in phase one. From this first-phase
information, three of the strata had sample units that contained buttercups.
In the second phase, these three strata were surveyed completely, and the
total final sample size was therefore (3 × 25) + (9 × 3) = 102.
For the three strata that did trigger adaptive sampling, π
h
, the probability
that whole stratum is selected (Equation 3.6) is:
18
3
25
3
π= −
1
=
0.645
,
5
11
3
25
3
π= −
1
=
0.928
, and
6
11
3
25
3
π= −
1
=
0.928
.
7
In the other nine strata, no plants were observed. The estimate of the total
number of plants using Equation (3.5) is:
3
∗
∑
y
ˆ
τ=
h
π
h
h
1
=
15
0.645
66
0.928
73
0.928
=
+
+
=
172.99
.
The estimated variance of this estimate from Equation (3.7) is:
3
(1
)
∗
2
∑
−π
π
y
·
Var[
ˆ
]
hh
τ=
2
h
h
=
1
2
2
2
(1 0.645)15
0.645
−
(1 0.928)66
0.928
−
(1 0.928)73
0.928
−
=
+
+
2
2
2
=
998.08
.
3.4 Discussion
Adaptive sampling is a broad term that encompasses a wide range of designs.
The essential feature of the designs for rare and clustered populations that are
