# Another meta-sandwich

In a previous post, I provided some code to do robust variance estimation with `metafor`

and `sandwich`

.
Here’s another example, replicating some more of the calculations from Tanner-Smith & Tipton (2013).
(See here for the complete code.)

As a starting point, here are the results produced by the `robumeta`

package:

```
library(grid)
library(robumeta)
data(corrdat)
rho <- 0.8
HTJ <- robu(effectsize ~ males + college + binge,
data = corrdat,
modelweights = "CORR", rho = rho,
studynum = studyid,
var.eff.size = var, small = FALSE)
HTJ
```

```
## RVE: Correlated Effects Model
##
## Model: effectsize ~ males + college + binge
##
## Number of studies = 39
## Number of outcomes = 172 (min = 1 , mean = 4.41 , median = 4 , max = 18 )
## Rho = 0.8
## I.sq = 75.08352
## Tau.sq = 0.1557714
##
## Estimate StdErr t-value dfs P(|t|>) 95% CI.L 95% CI.U Sig
## 1 X.Intercept. 0.31936 0.27784 1.149 35 0.258 -0.2447 0.88340
## 2 males -0.00331 0.00376 -0.882 35 0.384 -0.0109 0.00431
## 3 college 0.41226 0.18685 2.206 35 0.034 0.0329 0.79159 **
## 4 binge 0.13774 0.12586 1.094 35 0.281 -0.1178 0.39326
## ---
## Signif. codes: < .01 *** < .05 ** < .10 *
## ---
```

To exactly re-produce the results with `metafor`

, I’ll need to use the weights proposed by HTJ. In their approach to the correlated effects case, effect size \(i\) from study \(j\) receives weight equal to \(\left[\left(v_{\cdot j} + \hat\tau^2\right)(1 + (k_j - 1) \rho)\right]^{-1}\), where \(v_{\cdot j}\) is the average sampling variance of the effect sizes from study \(j\), \(\hat\tau^2\) is an estimate of the between-study variance, \(k_j\) is the number of correlated effects in study \(j\), and \(\rho\) is a user-specified value of the intra-study correlation. However, it appears that `robumeta`

actually uses a slightly different set weights, which are equivalent to taking \(\rho = 1\). I calculate the latter weights, fit the model in `metafor`

, and output the robust standard errors and \(t\)-tests:

```
devtools::source_gist(id = "11144005", filename = "metafor-sandwich.R")
corrdat <- within(corrdat, {
var_mean <- tapply(var, studyid, mean)[studyid]
k <- table(studyid)[studyid]
var_HTJ <- as.numeric(k * (var_mean + as.numeric(HTJ$mod_info$tau.sq)))
})
meta1 <- rma.mv(effectsize ~ males + college + binge,
V = var_HTJ,
data = corrdat, method = "FE")
meta1$cluster <- corrdat$studyid
RobustResults(meta1)
```

```
##
## t test of coefficients:
##
## Estimate Std. Error t value Pr(>|t|)
## intrcpt 0.3193586 0.2778360 1.1494 0.25816
## males -0.0033143 0.0037573 -0.8821 0.38374
## college 0.4122631 0.1868489 2.2064 0.03401 *
## binge 0.1377393 0.1258637 1.0944 0.28127
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
```

One could specify a similar (though not exactly identical model) in `metafor`

as follows. In the HTJ approach, \(\rho\) represents the total correlation induced by both the within-study sampling error and intra-study correlation in true effects. In contrast, the `metafor`

approach would take \(\rho\) to be correlation due to within-study sampling error alone. I’ll first need to create a block-diagonal covariance matrix given a user-specified value of \(\rho\).

```
library(Matrix)
equicorr <- function(x, rho) {
corr <- rho + (1 - rho) * diag(nrow = length(x))
tcrossprod(x) * corr
}
covMat <- as.matrix(bdiag(with(corrdat, tapply(var_mean, studyid, equicorr, rho = 0.8, simplify = FALSE))))
```

Passing this block-diagonal covariance matrix to `rma.mv`

, I now estimate the model

\[T_{ij} = \mathbf{X}_{ij} \beta + \nu_i + e_{ij},\]

where \(Var(\nu_i) = \sigma^2\), \(Var(e_{ij}) = v_{ij}\), and \(Cor(e_{ij}, e_{ik}) = \rho\). Note that \(\sigma^2\) is now estimated via REML.

```
meta2 <- rma.mv(yi = effectsize ~ males + college + binge,
V = covMat, random = ~ 1 | studyid,
data = corrdat,
method = "REML")
c(sigma.sq = meta2$sigma2)
```

```
## sigma.sq
## 0.2477825
```

The between-study heterogeneity estimate is considerably larger than the moment estimate from `robumeta`

. Together with the difference in weighting, this leads to some changes in the coefficient estimates and their estimated precision:

`RobustResults(meta2)`

```
##
## t test of coefficients:
##
## Estimate Std. Error t value Pr(>|t|)
## intrcpt -0.8907096 0.4148219 -2.1472 0.038783 *
## males 0.0163074 0.0055805 2.9222 0.006052 **
## college 0.3180139 0.2273396 1.3988 0.170658
## binge -0.0984026 0.0897269 -1.0967 0.280265
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
```

It is important to keep in mind that the estimate of between-study heterogeneity depends on the posited model for the covariance structure, including the assumed value of \(\rho\). HTJ recommend conducting sensitivity analysis across a range of values for the within-study effect correlation. Re-calculating the value of \(\sigma^2\) for \(\rho\) between 0.0 and 0.9 yields the following:

```
sigma2 <- function(rho) {
covMat <- as.matrix(bdiag(with(corrdat, tapply(var_mean, studyid, equicorr, rho = rho, simplify = FALSE))))
rma.mv(yi = effectsize ~ males + college + binge,
V = covMat, random = ~ 1 | studyid,
data = corrdat,
method = "REML")$sigma2
}
rho_sens <- seq(0,0.9,0.1)
sigma2_sens <- sapply(rho_sens, sigma2)
cbind(rho = rho_sens, sigma2 = round(sigma2_sens, 4))
```

```
## rho sigma2
## [1,] 0.0 0.2519
## [2,] 0.1 0.2513
## [3,] 0.2 0.2507
## [4,] 0.3 0.2502
## [5,] 0.4 0.2497
## [6,] 0.5 0.2492
## [7,] 0.6 0.2487
## [8,] 0.7 0.2482
## [9,] 0.8 0.2478
## [10,] 0.9 0.2474
```

The between-study heterogeneity is quite insensitive to the assumed value of \(\rho\).

The difference between the results based on `metafor`

versus on `robumeta`

appears to be due to the subtle difference in the weighting approach: `metafor`

uses block-diagonal weights that contain off-diagonal terms for effects drawn from a common study, whereas `robumeta`

uses entirely diagonal weights.