The resulting model can
be used by indirect_effect(),
cond_indirect_effects(), or
cond_indirect() as a path method,
as if fitted by lavaan::sem().
Arguments
- ...
The
lm()outputs to be grouped in a list.
Value
It returns an lm_list-class
object that forms a path model
represented by a set of regression
models. This class has a summary
method that shows the summary of
each regression model stored (see
summary.lm_list()), and a print
method that prints the models stored
(see print.lm_list()).
Details
If a path model with
mediation and/or moderation is fitted
by a set of regression models using
lm(), this function can combine
them to an object of the class
lm_list that represents a path
model, as one fitted by structural
equation model functions such as
lavaan::sem(). This class of object
can be used by some functions, such
as indirect_effect(),
cond_indirect_effects(), and
cond_indirect() as if they were the
output of fitting a path model, with
the regression coefficients treated
as path coefficients.
The regression outputs to be combined need to meet the following requirements:
All models must be connected to at least one another model. That is, a regression model must either have (a) at least on predictor that is the outcome variable of another model, or (b) its outcome variable the predictor of another model.
All models must be fitted to the same sample. This implies that the sample size must be the same in all analysis.
See also
summary.lm_list() and
print.lm_list() for related
methods, indirect_effect() and
cond_indirect_effects() which
accept lm_list-class objects as
input.
Examples
data(data_serial_parallel)
lm_m11 <- lm(m11 ~ x + c1 + c2, data_serial_parallel)
lm_m12 <- lm(m12 ~ m11 + x + c1 + c2, data_serial_parallel)
lm_m2 <- lm(m2 ~ x + c1 + c2, data_serial_parallel)
lm_y <- lm(y ~ m11 + m12 + m2 + x + c1 + c2, data_serial_parallel)
# Join them to form a lm_list-class object
lm_serial_parallel <- lm2list(lm_m11, lm_m12, lm_m2, lm_y)
lm_serial_parallel
#>
#> The model(s):
#> m11 ~ x + c1 + c2
#> m12 ~ m11 + x + c1 + c2
#> m2 ~ x + c1 + c2
#> y ~ m11 + m12 + m2 + x + c1 + c2
#>
summary(lm_serial_parallel)
#>
#>
#> Model:
#> m11 ~ x + c1 + c2
#> Estimate Std. Error t value Pr(>|t|)
#> (Intercept) 11.4546 1.1258 10.17 < 2e-16 ***
#> x 0.8001 0.0953 8.39 4.2e-13 ***
#> c1 0.0855 0.1020 0.84 0.404
#> c2 -0.2444 0.1002 -2.44 0.017 *
#> ---
#> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#> R-square = 0.459. Adjusted R-square = 0.442. F(3, 96) = 27.148, p < .001
#>
#> Model:
#> m12 ~ m11 + x + c1 + c2
#> Estimate Std. Error t value Pr(>|t|)
#> (Intercept) 9.8742 1.5048 6.56 2.8e-09 ***
#> m11 0.4652 0.0946 4.92 3.7e-06 ***
#> x 0.1146 0.1164 0.98 0.3274
#> c1 0.1934 0.0949 2.04 0.0444 *
#> c2 -0.2848 0.0957 -2.97 0.0037 **
#> ---
#> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#> R-square = 0.469. Adjusted R-square = 0.446. F(4, 95) = 20.963, p < .001
#>
#> Model:
#> m2 ~ x + c1 + c2
#> Estimate Std. Error t value Pr(>|t|)
#> (Intercept) 2.354 1.236 1.91 0.06 .
#> x 0.435 0.105 4.15 7.1e-05 ***
#> c1 0.178 0.112 1.59 0.12
#> c2 -0.167 0.110 -1.52 0.13
#> ---
#> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#> R-square = 0.196. Adjusted R-square = 0.171. F(3, 96) = 7.812, p < .001
#>
#> Model:
#> y ~ m11 + m12 + m2 + x + c1 + c2
#> Estimate Std. Error t value Pr(>|t|)
#> (Intercept) -1.791908 4.613263 -0.39 0.69859
#> m11 0.203249 0.266930 0.76 0.44832
#> m12 0.519112 0.255389 2.03 0.04494 *
#> m2 0.838632 0.217639 3.85 0.00021 ***
#> x 0.071421 0.317264 0.23 0.82238
#> c1 -0.000114 0.244934 0.00 0.99963
#> c2 -0.069787 0.253231 -0.28 0.78348
#> ---
#> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#> R-square = 0.315. Adjusted R-square = 0.271. F(6, 93) = 7.133, p < .001
# Compute indirect effect from x to y through m11 and m12
outm11m12 <- cond_indirect(x = "x", y = "y",
m = c("m11", "m12"),
fit = lm_serial_parallel)
outm11m12
#>
#> == Indirect Effect ==
#>
#> Path: x -> m11 -> m12 -> y
#> Indirect Effect: 0.193
#>
#> Computation Formula:
#> (b.m11~x)*(b.m12~m11)*(b.y~m12)
#>
#> Computation:
#> (0.80006)*(0.46521)*(0.51911)
#>
#> Coefficients of Component Paths:
#> Path Coefficient
#> m11~x 0.800
#> m12~m11 0.465
#> y~m12 0.519
#>
# Compute indirect effect from x to y
# through m11 and m12 with bootstrapping CI
# R should be at least 2000 or even 5000 in read study.
# In real research, parallel and progress can be omitted.
# They are est to TRUE by default.
outm11m12 <- cond_indirect(x = "x", y = "y",
m = c("m11", "m12"),
fit = lm_serial_parallel,
boot_ci = TRUE,
R = 100,
seed = 1234,
parallel = FALSE,
progress = FALSE)
outm11m12
#>
#> == Indirect Effect ==
#>
#> Path: x -> m11 -> m12 -> y
#> Indirect Effect: 0.193
#> 95.0% Bootstrap CI: [-0.110 to 0.487]
#>
#> Computation Formula:
#> (b.m11~x)*(b.m12~m11)*(b.y~m12)
#>
#> Computation:
#> (0.80006)*(0.46521)*(0.51911)
#>
#>
#> Percentile confidence interval formed by nonparametric bootstrapping
#> with 100 bootstrap samples.
#>
#> Coefficients of Component Paths:
#> Path Coefficient
#> m11~x 0.800
#> m12~m11 0.465
#> y~m12 0.519
#>