category.est.fcn(psurvey.analysis)S-PLUS Documentation
Category Proportion and Total Estimates

Category Proportion and Total Estimates

DESCRIPTION:

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.

USAGE:

category.est.fcn(catvar, wgt, x=NULL, y=NULL, stratum=NULL,
  cluster=NULL, N.cluster=NULL, wgt1=NULL, x1=NULL, y1=NULL,
  popsize=NULL, stage1size=NULL, support=NULL, swgt=NULL,
  swgt1=NULL, unitsize=NULL, type="Category", vartype="Local",
  conf=95, check.ind = TRUE)

REQUIRED ARGUMENTS:

catvar
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.

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.

Author

Tom Kincaid Kincaid.Tom@epa.gov

REFERENCES:

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.

EXAMPLES:

catvar <- rep(c("north", "south", "east", "west"), rep(25, 4))
wgt <- runif(100, 10, 100)
category.est.fcn(catvar, wgt, vartype="SRS")

x <- runif(100)
y <- runif(100)
category.est.fcn(catvar, wgt, x, y)

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