EnvStats (version 2.1.0)

gofGroup.object: S3 Class "gofGroup"

Description

Objects of S3 class "gofGroup" are returned by the EnvStats function gofGroupTest.

Value

• Required Components The following components must be included in a legitimate list of class "gofGroup".
• distribution
  a character string indicating the name of the assumed distribution (see Distribution.df).
• dist.abb
  a character string containing the abbreviated name of the distribution (see Distribution.df).
• statistic
  a numeric scalar with a names attribute containing the name and value of the goodness-of-fit statistic.
• sample.size
  a numeric scalar containing the number of non-missing observations in the sample used for the goodness-of-fit test.
• parameters
  numeric vector with a names attribute containing the name(s) and value(s) of the parameter(s) associated with the test statistic given in the statistic component.
• p.value
  numeric scalar containing the p-value associated with the goodness-of-fit statistic.
• alternative
  character string indicating the alternative hypothesis.
• method
  character string indicating the name of the goodness-of-fit test (e.g., "Wilk-Shapiro GOF (Normal Scores)").
• data.name
  character string indicating the name of the data object used for the goodness-of-fit test.
• grouping.variable
  character string indicating the name of the variable defining the groups.
• bad.obs
  numeric vector indicating the number of missing (NA), undefined (NaN) and/or infinite (Inf, -Inf) values that were removed from each group and the grouping variable prior to performing the goodness-of-fit test.
• n.groups
  numeric scalar containing the number of groups.
• group.names
  character vector containing the levels of the grouping variable, i.e., the names of each of the groups.
• group.scores
  numeric vector containing the individual statistics for each group.
• Optional Component The following component is included when gofGroupTest is called with a formula for the first argument and a data argument.
• parent.of.data
  character string indicating the name of the object supplied in the data argument.

Methods

Generic functions that have methods for objects of class "gofGroup" include: print, plot.

Details

Objects of S3 class "gofGroup" are lists that contain information about the assumed distribution, the estimated or user-supplied distribution parameters, and the test statistic and p-value.

See Also

gofGroupTest, print.gofGroup, plot.gofGroup, Goodness-of-Fit Tests, Distribution.df.

Examples

# Create an object of class "gofGroup", then print it out. 

  # Example 10-4 of USEPA (2009, page 10-20) gives an example of 
  # simultaneously testing the assumption of normality for nickel 
  # concentrations (ppb) in groundwater collected at 4 monitoring 
  # wells over 5 months.  The data for this example are stored in 
  # EPA.09.Ex.10.1.nickel.df.

  gofGroup.obj <- gofGroupTest(Nickel.ppb ~ Well, 
    data = EPA.09.Ex.10.1.nickel.df)

  mode(gofGroup.obj) 
  #[1] "list" 

  class(gofGroup.obj) 
  #[1] "gofGroup" 

  names(gofGroup.obj) 
  # [1] "distribution"      "dist.abb"          "statistic"        
  # [4] "sample.size"       "parameters"        "p.value"          
  # [7] "alternative"       "method"            "data.name"        
  #[10] "grouping.variable" "parent.of.data"    "bad.obs"          
  #[13] "n.groups"          "group.names"       "group.scores"

  gofGroup.obj 
  #Results of Group Goodness-of-Fit Test
  #-------------------------------------
  #
  #Test Method:                     Wilk-Shapiro GOF (Normal Scores)
  #
  #Hypothesized Distribution:       Normal
  #
  #Data:                            Nickel.ppb
  #
  #Grouping Variable:               Well
  #
  #Data Source:                     EPA.09.Ex.10.1.nickel.df
  #
  #Number of Groups:                4
  #
  #Sample Sizes:                    Well.1 = 5
  #                                 Well.2 = 5
  #                                 Well.3 = 5
  #                                 Well.4 = 5
  #
  #Test Statistic:                  z (G) = -3.658696
  #
  #P-values for
  #Individual Tests:                Well.1 = 0.03510747
  #                                 Well.2 = 0.02385344
  #                                 Well.3 = 0.01120775
  #                                 Well.4 = 0.10681461
  #
  #P-value for
  #Group Test:                      0.0001267509
  #
  #Alternative Hypothesis:          At least one group
  #                                 does not come from a
  #                                 Normal Distribution.  

  #==========

  # Extract the p-values
  #---------------------

  gofGroup.obj$p.value
  #      Well.1       Well.2       Well.3       Well.4        z (G) 
  #0.0351074733 0.0238534406 0.0112077511 0.1068146088 0.0001267509 

  #==========

  # Plot the results of the test
  #-----------------------------

  dev.new()
  plot(gofGroup.obj)

  #==========

  # Clean up
  #---------
  rm(gofGroup.obj)
  graphics.off()