OLStraj {OLStrajr}

OLStraj

Description

Implements the OLS trajectory analysis method as detailed in Carrig et al (2004). The method uses case-by-case ordinary least squares (OLS) regression to estimate individual growth curves over time. The function provides options for group-level and individual-level plots and accommodates linear and quadratic models.

Usage

OLStraj(
  data,
  idvarname = "id",
  predvarname = "time",
  outvarname = "score",
  varlist = c("anti1", "anti2", "anti3", "anti4"),
  timepts = c(0, 1, 2, 3),
  inclmiss = FALSE,
  level = "both",
  regtype = "lin",
  numplot = NULL,
  hist = TRUE,
  int_bins = 30,
  lin_bins = 30,
  quad_bins = 30,
  box = TRUE,
  outds = TRUE,
  ...
)

Arguments

data

A data frame

idvarname

A quoted variable name identifying the column in data which serves as the case identifier

predvarname

A quoted predictor variable label.

outvarname

A quoted outcome variable label.

varlist

A vector of quoted variable names found in data

timepts

A vector specifying how time points should be coded

inclmiss

A logical specifying whether or not to use complete cases. Set inclmiss to FALSE in order to filter data down to complete cases.

level

Control which OLS trajectory plots to show. If level is set to "grp" then only group level plots will be shown, if level is set to "ind" then only individual level plots will be shown, and if level is set to "both" then both group and individual level plots will be shown.

regtype

Set regtype to "quad" to include quadratic term in the cbc_lm call or set regtype to "lin" to exclude the quadratic term. Use regtype = "both" to include the quadratic term in the cbc_lm call and to include both linear and quadratic terms on the individual OLS-estimated trajectory plots.

numplot

Specify an integer to subset the number of cases used in OLStraj

hist

Set hist to TRUE to include histograms or FALSE to exclude

int_bins

Set the number of bins for the intercept term's histogram

lin_bins

Set the number of bins for the linear term's histogram

quad_bins

Set the number of bins for the quadratic term's histogram

box

Set box to TRUE to include boxplots or FALSE to exclude

outds

Set outds to TRUE to include the output as a data frame. Output will contain original data used in the OLStraj algorithm with the parameter estimates obtained from cbc_lm

...

Pass additional arguments to cbc_lm

Value

A list containing an output data frame (if outds is set to TRUE), the selected plots, and the case-by-case regression model object.

References

Carrig, M.M., Wirth, R.J., & Curran, P.J. (2004). A SAS Macro for Estimating and Visualizing Individual Growth Curves. Structural Equation Modeling: A Multidisciplinary Journal, 11(1), 132-149. doi:10.1207/S15328007SEM1101_9

Examples

  df <- data.frame(id = c(1,2,3,4,5),
                   var1 = c(3,7,4,5,8),
                   var2 = c(7,3,9,4,7),
                   var3 = c(8,5,3,9,7),
                   var4 = c(1,5,3,9,30))

  olstraj_out <- OLStraj(data = df,
                         varlist = c("var1", "var2", "var3", "var4"),
                         regtype = "quad",
                         int_bins = 5,
                         lin_bins = 5,
                         quad_bins = 5)