Agriculture Reference
In-Depth Information
P ¼
m
1
To obtain the rapid estimate of the intensity of
a disease in a crop field, one may locate “
n
”
n
1
subplots (say
9 one each in every direction
and one at center) in a pseudorandom manner,
each plot being a square of the same area, say,
“
n ¼
and an unbiased estimator of the variance of
P
is
P
P
a
.” The square may be of side 1 or 2 m. Let
p
i
¼
1
n
1
V
P
:
1
be the damaged proportion of the crop in the
I
th
ðn
2
Þ
N
P
n
i¼
1
p
i
would be
the required estimate. The total area damaged
in the field would be estimated as
A
p
¼
a
1
n
plot,
I ¼
1,
...
,
n
. Then
p ¼
p
6.2.1.10 Sampling Technique for Rapid
Assessment (STRA)
In exigencies like flood, diseases, tsunami, and
Aila, we may not get enough time, money, or
manpower to undertake a usual sampling tech-
nique, but in any way, we need a reliable estimate
on some population parameters like damage of
crops, houses, cattle, and human lives in a very
short time so that the next suitable steps may be
taken. Thus, to obtain an estimate of the total
area damaged due to the outbreak of a particular
pest in block, one may select “
A
is the area of the field. The estimated
variance would be
where
2
vðpÞ:
vð A
p
Þ¼
A
a
The sampling techniques for rapid assessment
(STRA) may also be used for obtaining estimates
of the yields of various crops.
n
” points (“
n
”
being small, say,
15) haphazardly at differ-
ent locations and calculate the mean intensity of
outbreak from a rectangular area of, say, A
n ¼
6.2.2 Non-probability Sampling
¼
5m
2
at these points. Let
I
1
,
...
I
n
be the
5
,
1.
Quota Sampling
: Each interviewer is assigned
to interview a fixed number of respondents
(quota) that are taken as representation of the
whole sample.
If these are different groups in a population
and a sample is drawn in such a way that a
fixed number of units from different groups
required to be included in that sample, say,
intensities of pest
infestation in these “
n
”
I ¼
pseudorandomly selected rectangles and
1
n
P
n
i¼
1
I
i
be the sample mean. Then the estimated
infestation would be
I
A
a
n
1
,
M ¼
(7.1)
n
2
,
...
,
n
i
from the
i
th group to provide ran-
dom sample of size
n ¼ n
1
+
n
2
+
...
+
n
i
.
But
where
A
is the area (in m
2
) under the block.
these
n
i
number of units are
selected by the interviewer in a nonrandom
fashion.
This procedure of sampling is less costly, is
convenient, does not require any sampling
frame, and gives quick reply. But as has
been mentioned earlier, it is criticized heavily
because of its nonrandom selection of
elements. The success of the entire procedure
depends on the skill and personal efficiency of
the interviewer.
n
1
,
n
2
,
...
,
NW
N
NE
W
E
C
S W
S
SE
2.
Judgment Sampling
: Basic to this type of sam-
pling is to select a sample of desired size,
