bruceR (version 0.7.2)

HLM_summary: Tidy report of HLM (lmer and glmer models).

Description

Nice report of Hierarchical Linear Model (HLM), also known as Multilevel Linear Model (MLM) or Linear Mixed Model (LMM). HLM, MLM, or LMM (the same) refers to a model with nested data (e.g., Level-1: participants, Level-2: city; or Level-1: repeated-measures within a participant, Level-2: participants).

Usage

HLM_summary(
  model = NULL,
  level2.predictors = NULL,
  vartypes = NULL,
  test.rand = FALSE,
  digits = 3,
  nsmall = digits,
  ...
)

Arguments

model

A model fitted by lmer or glmer function using the lmerTest package.

level2.predictors

[only for lmer] [optional] Default is NULL. If you have predictors at level 2, besides putting them into the formula in the lmer function as usual, you may also define here the level-2 grouping/clustering variables and corresponding level-2 predictor variables.

*** Example: level2.predictors="School: W1 + W2; House: 1", where School and House are two grouping variables, W1 & W2 are school-level predictors, and there is no house-level predictor.

*** If there is no level-2 predictor in the formula of lmer, just leave this parameter blank.

vartypes

[only for lmer] Manually setting variable types. Needless in most situations.

test.rand

[only for lmer] TRUE or FALSE (default). Test random effects (i.e., variance components) by using the likelihood-ratio test (LRT), which is asymptotically chi-square distributed. For large datasets, it is much time-consuming.

digits, nsmall

Number of decimal places of output. Default is 3. But for some statistics (e.g., R^2, ICC), to provide more precise information, we fix the decimal places to 5.

...

Other optional parameters. You may re-define formula, data, or family.

Value

No return value.

Details

Hierarchical Linear Model (HLM), aka. Multilevel Linear Model (MLM) or Linear Mixed Model (LMM), is more complex than General Linear Model (GLM; i.e., OLS regression). Predictor variables at different levels may have five types:

1. Intercept

The overall intercept (\(\gamma_{00}\))

2. L1fixed

Level-1 predictor with fixed slope

3. L1random-GROUP-L1VAR

Level-1 predictor with random slopes nested with a grouping/clustering variable

4. L2-GROUP

Level-2 predictor (e.g., GDP per capita at city level), always with fixed slope unless there is also a level-3 structure.

*** NOTE: the current version of 'HLM_summary' function does not consider three-levels design, so you may only use this function in two-levels HLM or cross-classified HLM.

5. Cross-GROUP-L1VAR

Cross-level interaction consisting of level-1 and level-2 predictors

The degrees of freedom (df) of predictor variables in HLM vary across different levels and also depend on the variable types. However, different software use different estimation methods and thus provide somewhat different dfs, which may be confusing. Whereas the lmerTest package in R provides dfs that are estimated by the Satterthwaite's (1946) approximation (i.e., a data-driven approach without defining variable types), the HLM software provides dfs that totally depend on the variable types (i.e., a theory-driven approach).

References

Hox, J. J. (2010). Multilevel analysis: Techniques and applications (2nd ed.). New York, NY: Routledge. 10.4324/9780203852279

Nakagawa, S., & Schielzeth, H. (2013). A general and simple method for obtaining R^2 from generalized linear mixed-effects models. Methods in Ecology and Evolution, 4, 133-142. 10.1111/j.2041-210x.2012.00261.x

Xu, R. (2003). Measuring explained variation in linear mixed effects models. Statistics in Medicine, 22, 3527-3541. 10.1002/sim.1572

See Also

GLM_summary, regress

Examples

# NOT RUN {
library(lmerTest)

## Example 1: data from lme4::sleepstudy
# (1) 'Subject' is a grouping/clustering variable
# (2) 'Days' is a level-1 predictor nested within 'Subject'
# (3) No level-2 predictors
m1=lmer(Reaction ~ (1 | Subject), data=sleepstudy)
m2=lmer(Reaction ~ Days + (1 | Subject), data=sleepstudy)
m3=lmer(Reaction ~ Days + (Days | Subject), data=sleepstudy)
HLM_summary(m1)
HLM_summary(m2)
HLM_summary(m3)

## Example 2: data from lmerTest::carrots
# (1) 'Consumer' is a grouping/clustering variable
# (2) 'Sweetness' is a level-1 predictor
# (3) 'Age' and 'Frequency' are level-2 predictors
hlm.1=lmer(Preference ~ Sweetness + Age + Frequency +
             (1 | Consumer), data=carrots)
hlm.2=lmer(Preference ~ Sweetness + Age + Frequency +
             (Sweetness | Consumer) + (1 | Product), data=carrots)
HLM_summary(hlm.1, level2.predictors="Consumer: Age + Frequency")
HLM_summary(hlm.2, level2.predictors="Consumer: Age + Frequency")
anova(hlm.1, hlm.2)
# }