This function estimates proportion (expressed as percent) and size of a
resource in each of a set of categories and can also be used to estimate
proportion and size for site status categories. Upper and lower confidence
bounds also are estimated.
the category variable value or site status for each site.
wgt
the final adjusted weight (inverse of the sample inclusion
probability) for each site, which is either the weight for a
single-stage sample or the stage two weight for a two-stage sample.
x
x-coordinate for location for each site, which is either the
x-coordinate for a single-stage sample or the stage two
x-coordinate for a two-stage sample. The default is NULL.
y
y-coordinate for location for each site, which is either the
y-coordinate for a single-stage sample or the stage two
y-coordinate for a two-stage sample. The default is NULL.
OPTIONAL ARGUMENTS:
stratum
the stratum for each site. The default is NULL.
cluster
the stage one sampling unit (primary sampling unit or cluster)
code for each site. The default is NULL.
N.cluster
the number of stage one sampling units in the resource, which
is required for calculation of finite and continuous population
correction factors for a two-stage sample. For a stratified sample
this variable must be a vector containing a value for each stratum and
must have the names attribute set to identify the stratum codes. The
default is NULL.
wgt1
the final adjusted stage one weight for each site. The default
is NULL.
x1
the stage one x-coordinate for location for each site. The default
is NULL.
y1
the stage one y-coordinate for location for each site. The default
is NULL.
popsize
the known size of the resource - the total number of sampling
units of a discrete resource or the measure of a continuous resource,
which is required for calculation of finite and continuous population
correction factors for a single-stage sample. This variable is also
used to adjust estimators for the known size of a resource. For a
stratified sample this variable must be a vector containing a value
for each stratum and must have the names attribute set to identify the
stratum codes. The default is NULL.
stage1size
the known size of the stage one sampling units of a two-
stage sample, which is required for calculation of finite and
continuous population correction factors for a two-stage sample and
must have the names attribute set to identify the stage one sampling
unit codes. For a stratified sample, the names attribute must be set
to identify both stratum codes and stage one sampling unit codes using
a convention where the two codes are separated by the # symbol, e.g.,
"Stratum 1#Cluster 1". The default is NULL.
support
the support value for each site - the value one (1) for a
site from a discrete resource or the measure of the sampling unit
associated with a site from a continuous resource, which is required
for calculation of finite and continuous population correction
factors. The default is NULL.
swgt
the size-weight for each site, which is the stage two size-weight
for a two-stage sample. The default is NULL.
swgt1
the stage one size-weight for each site. The default is NULL.
unitsize
the known sum of the size-weights of the resource, which for a
stratified sample must be a vector containing a value for each stratum
and must have the names attribute set to identify the stratum codes.
The default is NULL.
type
the type of response variable, where "Status" = site status and
"Category" = resource category. The default is "Category".
vartype
the choice of variance estimator, where "Local" = local mean
estimator and "SRS" = SRS estimator. The default is "Local".
conf
the confidence level. The default is 95%.
check.ind
a logical value that indicates whether compatability
checking of the input values is conducted, where TRUE = conduct
compatibility checking and FALSE = do not conduct compatibility
checking. The default is TRUE.
warn.ind
a logical value that indicates whether warning messages were
generated, where TRUE = warning messages were generated and FALSE = warning
messages were not generated. The default is NULL.
warn.df
a data frame for storing warning messages. The default is
NULL.
warn.vec
a vector that contains names of the population type, the
subpopulation, and an indicator. The default is NULL.
VALUE:
A list containing the following components:
Prop
a data frame containing the proportion estimates
Size
a data frame containing the size estimates
SIDE EFFECTS:
None
DETAILS:
Proportion estimates are calculated using the Horvitz-Thompson ratio estimator,
i.e., the ratio of two Horvitz-Thompson estimators. The numerator of the ratio
estimates the size of the site status category. The denominator of the ratio
estimates the size of the resource. Variance estimates for the proportion
estimates are calculated using either the local mean variance estimator or the
simple random sampling (SRS) variance estimator. The choice of variance
estimator is subject to user control. The local mean variance estimator
requires the x-coordinate and the y-coordinate of each site. The
SRS variance estimator uses the independent random sample approximation
to calculate joint inclusion probabilities. Confidence bounds are calculated
using a Normal distribution multiplier. For a discrete resource size is
the number of units in the resource. For an extensive resource size is the
measure (extent) of the resource, i.e., length, area, or volume. Size
estimates are calculated using the Horvitz- Thompson estimator. Variance
estimates for the size estimates are calculated using either the local mean
variance estimator or the SRS variance estimator. The function can
accommodate a stratified sample. For a stratified sample, separate estimates
and standard errors are calculated for each stratum, which are used to produce
estimates and standard errors for all strata combined. Strata that contain a
single value are removed. For a stratified sample, when either the size of the
resource or the sum of the size-weights for the resource is provided for each
stratum, those values are used as stratum weights for calculating the
estimates and standard errors for all strata combined. In addition, when
either of those known values is provided for each stratum, size estimates are
obtained by multiplying the proportion estimate, i.e., the Horvitz-Thompson
ratio estimator, by the known value for the stratum. For a stratified sample
when neither the size of the resource nor the sum of the size-weights of the
resource is provided for each stratum, estimated values are used as stratum
weights for calculating the estimates and standard errors for all strata
combined. The function can accomodate single-stage and two-stage samples for
both stratified and unstratified sampling designs. Finite population and
continuous population correction factors can be utilized in variance estimation.
The function checks for compatibility of input values and removes missing values.
Diaz-Ramos, S., D.L. Stevens, Jr., and A.R. Olsen. (1996). EMAP
Statistical Methods Manual. EPA/620/R-96/XXX. Corvallis, OR: U.S.
Environmental Protection Agency, Office of Research and Development, National
Health Effects and Environmental Research Laboratory, Western Ecology
Division.