sjp.glmer: Plot estimates, predictions or effects of generalized linear mixed effects models

Description

By default, this function plots estimates (odds, risk or incidents ratios, i.e. exponentiated coefficients, depending on family and link function) with confidence intervals of either fixed effects or random effects of generalized linear mixed effects models (that have been fitted with the glmer-function of the lme4-package). Furthermore, this function also plots predicted probabilities / incidents or diagnostic plots.

Usage

sjp.glmer(fit, type = "re", vars = NULL, ri.nr = NULL, group.estimates = NULL, remove.estimates = NULL, emph.grp = NULL, sample.n = NULL, sort.est = NULL, title = NULL, legend.title = NULL, axis.labels = NULL, axis.title = NULL, geom.colors = "Set1", geom.size = NULL, show.values = TRUE, show.p = TRUE, show.ci = FALSE, show.legend = FALSE, show.intercept = FALSE, string.interc = "(Intercept)", fade.ns = FALSE, axis.lim = NULL, digits = 2, vline.type = 2, vline.color = "grey70", facet.grid = TRUE, free.scale = FALSE, y.offset = 0.1, prnt.plot = TRUE, ...)

Arguments

fit

a fitted model as returned by the glmer-function.

type

type of plot. Use one of following:

vars

numeric vector with column indices of selected variables or a character vector with variable names of selected variables from the fitted model, which should be used to plot estimates, fixed effects slopes (for lmer) or probability or incidents curves (for glmer) of random intercepts.

ri.nr

numeric vector. If type = "re" or type = "ri.slope", and fitted model has more than one random intercept, ri.nr indicates which random effects of which random intercept (or: which list elements of ranef) will be plotted. Default is NULL, so all random effects will be plotted.

group.estimates

numeric or character vector, indicating a group identifier for each estimate. Dots and confidence intervals of estimates are coloured according to their group association. See 'Examples'.

remove.estimates

character vector with coefficient names that indicate which estimates should be removed from the plot. remove.estimates = "est_name" would remove the estimate est_name. Default is NULL, i.e. all estimates are printed.

emph.grp

numeric vector with index numbers of grouping levels (from random effect). If type = "ri.slope" and facet.grid = FALSE, an integrated plot of predicted probabilities of fixed effects resp. fixed effects slopes for each grouping level is plotted. To better find certain groups, use this argument to emphasize these groups in the plot. See 'Examples'.

sample.n

numeric vector. only applies, if type = "rs.ri". If plot has many random intercepts (grouping levels), overplotting of regression lines may occur. In this case, consider random sampling of grouping levels. If sample.n is of length 1, a random sample of sample.n observation is selected to plot random intercepts. If sample.n is of length > 1, random effects indicated by the values in sample.n are selected to plot random effects. Use the latter option to always select a fixed, identical set of random effects for plotting (useful when ecomparing multiple models).

sort.est

determines in which way estimates are sorted in the plot:

If NULL (default), no sorting is done and estimates are sorted in order of model coefficients.
If sort.est = "sort.all", estimates are re-sorted for each coefficient (only applies if type = "re" and facet.grid = FALSE), i.e. the estimates of the random effects for each predictor are sorted and plotted to an own plot.
If type = "fe" or type = "fe.std", TRUE will sort estimates
If type = "re", specify a predictor's / coefficient's name to sort estimates according to this coefficient.

See 'Examples'.

title

character vector with one or more labels that are used as plot title.

legend.title

character vector, used as title for the plot legend. Note that only some plot types have legends (e.g. type = "pred" or when grouping estimates with group.estimates).

axis.labels

character vector with labels for the model terms, used as axis labels. For mixed models, should either be vector of fixed effects variable labels (if type = "fe" or type = "fe.std") or a vector of group (value) labels from the random intercept's categories (if type = "re").

axis.title

character vector of length one or two (depending on the plot function and type), used as title(s) for the x and y axis. If not specified, a default labelling is chosen.

geom.colors

user defined color palette for geoms. If group.estimates is not specified, must either be vector with two color values or a specific color palette code (see 'Details' in sjp.grpfrq). Else, if group.estimates is specified, geom.colors must be a vector of same length as groups. See 'Examples'.

geom.size

size resp. width of the geoms (bar width, line thickness or point size, depending on plot type and function). Note that bar and bin widths mostly need smaller values than dot sizes.

show.values

logical, whether values should be plotted or not.

show.p

logical, adds significance levels to values, or value and variable labels.

show.ci

logical, if TRUE, depending on type, a confidence interval or region is added to the plot.

show.legend

logical, if TRUE, and depending on plot type and function, a legend is added to the plot.

show.intercept

logical, if TRUE, the intercept of the fitted model is also plotted. Default is FALSE. For glm's, please note that due to exponential transformation of estimates, the intercept in some cases can not be calculated, thus the function call is interrupted and no plot printed.

string.interc

string, axis label of intercept estimate. Only applies, if show.intercept = TRUE and axis.labels is not NULL.

fade.ns

if TRUE, non significant estimates will be printed in slightly faded colors.

axis.lim

numeric vector of length 2, defining the range of the plot axis. Depending on plot type, may effect either x- or y-axis, or both. For multiple plot outputs (e.g., from type = "eff" or type = "slope" in sjp.glm), axis.lim may also be a list of vectors of length 2, defining axis limits for each plot (only if non-faceted).

digits

numeric, amount of digits after decimal point when rounding estimates and values.

vline.type

linetype of the vertical "zero point" line. Default is 2 (dashed line).

vline.color

color of the vertical "zero point" line. Default value is "grey70".

facet.grid

TRUE to arrange the lay out of of multiple plots in a grid of an integrated single plot. This argument calls facet_wrap or facet_grid to arrange plots. Use plot_grid to plot multiple plot-objects as an arranged grid with grid.arrange.

free.scale

if TRUE and facet.grid = TRUE, each facet grid gets its own fitted scale. If free.scale = FALSE, each facet in the grid has the same scale range.

y.offset

numeric, offset for text labels when their alignment is adjusted to the top/bottom of the geom (see hjust and vjust).

prnt.plot

logical, if TRUE (default), plots the results as graph. Use FALSE if you don't want to plot any graphs. In either case, the ggplot-object will be returned as value.

...

other arguments, passed down to the effect resp. allEffects function when type = "eff".

Value

(Insisibily) returns, depending on the plot type

The ggplot-object (plot). For multiple plots and if facet.grid = FALSE) a plot.list is returned.
A data frame data with the data used to build the ggplot-object(s), or a list of data frames (data.list).

Details

Examples

Run this code

library(lme4)
library(sjmisc)
# create binary response
sleepstudy$Reaction.dicho <- dicho(sleepstudy$Reaction, dich.by = "median")
# fit model
fit <- glmer(Reaction.dicho ~ Days + (Days | Subject),
             data = sleepstudy, family = binomial("logit"))

# simple plot
sjp.glmer(fit)

# sort by predictor Days
sjp.glmer(fit, sort.est = "Days")

data(efc)
# create binary response
efc$hi_qol <- dicho(efc$quol_5)
# prepare group variable
efc$grp = as.factor(efc$e15relat)
levels(x = efc$grp) <- get_labels(efc$e15relat)
# data frame for fitted model
mydf <- data.frame(hi_qol = to_factor(efc$hi_qol),
                   sex = to_factor(efc$c161sex),
                   education = to_factor(efc$c172code),
                   c12hour = efc$c12hour,
                   neg_c_7 = efc$neg_c_7,
                   grp = efc$grp)
# fit glmer
fit <- glmer(hi_qol ~ sex + c12hour + neg_c_7 + (1|grp),
             data = mydf, family = binomial("logit"))

# plot and sort fixed effects
sjp.glmer(fit, type = "fe", sort.est = TRUE)

# fit glmer, with categorical predictor with more than 2 levels
fit <- glmer(hi_qol ~ sex + education + c12hour + neg_c_7 + (1|grp),
             data = mydf, family = binomial("logit"))

# plot and sort fixed effects, axis labels automatically retrieved
sjp.glmer(fit, type = "fe", sort.est = TRUE)

# plot probability curves (predicted probabilities)
# for each covariate, grouped by random intercepts
# in integrated plots, emphasizing groups 1 and 4
sjp.glmer(fit, type = "ri.slope", emph.grp = c(1, 4), facet.grid = FALSE)

# plot probability curve (predicted probabilities)
# of fixed effect, only for coefficient "neg_c_7"
sjp.glmer(fit, type = "fe.slope", vars = "neg_c_7")

# plot predicted probabilities for response,
# related to model predictor, conditioned on random effects
sjp.glmer(fit, type = "pred", vars = "neg_c_7")

# plot predicted probabilities for response,
# related to model predictor, grouped
sjp.glmer(fit, type = "pred.fe", vars = c("neg_c_7", "sex"))
          
# non faceted, with ci           
sjp.glmer(fit, type = "pred.fe", vars = c("neg_c_7", "education"), 
          show.ci = TRUE, facet.grid = FALSE)