R: Representativeness of Observations in a Data Set

dataRep {Hmisc} | R Documentation

## Representativeness of Observations in a Data Set

### Description

These functions are intended to be used to describe how well a given set of new observations (e.g., new subjects) were represented in a dataset used to develop a predictive model. The `dataRep` function forms a data frame that contains all the unique combinations of variable values that existed in a given set of variable values. Cross–classifications of values are created using exact values of variables, so for continuous numeric variables it is often necessary to round them to the nearest `v` and to possibly curtail the values to some lower and upper limit before rounding. Here `v` denotes a numeric constant specifying the matching tolerance that will be used. `dataRep` also stores marginal distribution summaries for all the variables. For numeric variables, all 101 percentiles are stored, and for all variables, the frequency distributions are also stored (frequencies are computed after any rounding and curtailment of numeric variables). For the purposes of rounding and curtailing, the `roundN` function is provided. A `print` method will summarize the calculations made by `dataRep`, and if `long=TRUE` all unique combinations of values and their frequencies in the original dataset are printed.

The `predict` method for `dataRep` takes a new data frame having variables named the same as the original ones (but whose factor levels are not necessarily in the same order) and examines the collapsed cross-classifications created by `dataRep` to find how many observations were similar to each of the new observations after any rounding or curtailment of limits is done. `predict` also does some calculations to describe how the variable values of the new observations "stack up" against the marginal distributions of the original data. For categorical variables, the percent of observations having a given variable with the value of the new observation (after rounding for variables that were through `roundN` in the formula given to `dataRep`) is computed. For numeric variables, the percentile of the original distribution in which the current value falls will be computed. For this purpose, the data are not rounded because the 101 original percentiles were retained; linear interpolation is used to estimate percentiles for values between two tabulated percentiles. The lowest marginal frequency of matching values across all variables is also computed. For example, if an age, sex combination matches 10 subjects in the original dataset but the age value matches 100 ages (after rounding) and the sex value matches the sex code of 300 observations, the lowest marginal frequency is 100, which is a "best case" upper limit for multivariable matching. I.e., matching on all variables has to result on a lower frequency than this amount. A `print` method for the output of `predict.dataRep` prints all calculations done by `predict` by default. Calculations can be selectively suppressed.

### Usage

    dataRep(formula, data, subset, na.action)

    roundN(x, tol=1, clip=NULL)

    ## S3 method for class 'dataRep'
    print(x, long=FALSE, ...)

    ## S3 method for class 'dataRep'
    predict(object, newdata, ...)

    ## S3 method for class 'predict.dataRep'
    print(x, prdata=TRUE, prpct=TRUE, ...)

### Arguments

`formula` | a formula with no left-hand-side. Continuous numeric variables in need of rounding should appear in the formula as e.g. `roundN(x,5)` to have a tolerance of e.g. +/- 2.5 in matching. Factor or character variables as well as numeric ones not passed through `roundN` are matched on exactly.
`x` | a numeric vector or an object created by `dataRep`
`object` | the object created by `dataRep` or `predict.dataRep`
`data, subset, na.action` | standard modeling arguments. Default `na.action` is `na.delete`, i.e., observations in the original dataset having any variables missing are deleted up front.
`tol` | rounding constant (tolerance is actually `tol/2` as values are rounded to the nearest `tol`)
`clip` | a 2-vector specifying a lower and upper limit to curtail values of `x` before rounding
`long` | set to `TRUE` to see all unique combinations and frequency count
`newdata` | a data frame containing all the variables given to `dataRep` but not necessarily in the same order or having factor levels in the same order
`prdata` | set to `FALSE` to suppress printing `newdata` and the count of matching observations (plus the worst-case marginal frequency).
`prpct` | set to `FALSE` to not print percentiles and percents
`...` | unused

### Value

`dataRep` returns a list of class `"dataRep"` containing the collapsed data frame and frequency counts along with marginal distribution information. `predict` returns an object of class `"predict.dataRep"` containing information determined by matching observations in `newdata` with the original (collapsed) data.

### Side Effects

`print.dataRep` prints.

### Author(s)

Frank Harrell
Department of Biostatistics
Vanderbilt University School of Medicine
f.harrell@vanderbilt.edu

### See Also

`round`, `table`

### Examples

    set.seed(13)
    num.symptoms <- sample(1:4, 1000,TRUE)
    sex <- factor(sample(c('female','male'), 1000,TRUE))
    x    <- runif(1000)
    x[1] <- NA
    table(num.symptoms, sex, .25*round(x/.25))

    d <- dataRep(~ num.symptoms + sex + roundN(x,.25))
    print(d, long=TRUE)

    predict(d, data.frame(num.symptoms=1:3, sex=c('male','male','female'),
                          x=c(.03,.5,1.5)))

[Package Hmisc version 4.3-0 Index]