Mathematic operators for
'indirect'-class object, the output
of `indirect_effect()`

and
`cond_indirect()`

.

## Value

An 'indirect'-class object
with a list of effects stored. See
`indirect_effect()`

on details for
this class.

## Details

For now, only `+`

operator
and `-`

operator are supported. These
operators can be used to estimate and
test a function of effects between
the same pair of variables but along
different paths.

For example, they can be used to compute and test the total effects along different paths. They can also be used to compute and test the difference between the effects along two paths.

The operators will check whether an operation is valid. An operation is not valid if

the two paths do not start from the same variable,

the two paths do not end at the same variable, (c) a path appears in both objects,

moderators are involved but they are not set to the same values in both objects, and

bootstrap estimates stored in

`boot_out`

, if any, are not identical.Monte Carlo simulated estimates stored in

`mc_out`

, if any, are not identical.

## Examples

```
library(lavaan)
dat <- modmed_x1m3w4y1
mod <-
"
m1 ~ a1 * x + d1 * w1 + e1 * x:w1
m2 ~ m1 + a2 * x
y ~ b1 * m1 + b2 * m2 + cp * x
"
fit <- sem(mod, dat,
meanstructure = TRUE, fixed.x = FALSE,
se = "none", baseline = FALSE)
est <- parameterEstimates(fit)
hi_w1 <- mean(dat$w1) + sd(dat$w1)
# Examples for cond_indirect():
# Conditional effect from x to m1 when w1 is 1 SD above mean
out1 <- cond_indirect(x = "x", y = "y", m = c("m1", "m2"),
wvalues = c(w1 = hi_w1), fit = fit)
out2 <- cond_indirect(x = "x", y = "y", m = c("m2"),
wvalues = c(w1 = hi_w1), fit = fit)
out3 <- cond_indirect(x = "x", y = "y",
wvalues = c(w1 = hi_w1), fit = fit)
out12 <- out1 + out2
out12
#>
#> == Conditional Indirect Effect ==
#>
#> Path: x -> m1 -> m2 -> y
#> Path: x -> m2 -> y
#> Moderators: w1
#> Function of Effects: 0.082
#> When: w1 = 1.228
#>
#> Computation of the Function of Effects:
#> (x->m1->m2->y)
#> +(x->m2->y)
#>
out123 <- out1 + out2 + out3
out123
#>
#> == Conditional Indirect Effect ==
#>
#> Path: x -> m1 -> m2 -> y
#> Path: x -> m2 -> y
#> Path: x -> y
#> Moderators: w1
#> Function of Effects: 0.394
#> When: w1 = 1.228
#>
#> Computation of the Function of Effects:
#> ((x->m1->m2->y)
#> +(x->m2->y))
#> +(x->y)
#>
coef(out1) + coef(out2) + coef(out3)
#> y~x
#> 0.39405
```