ds.lmerSLMA: Fits Linear Mixed-Effect model via Study-Level Meta-Analysis

In datashield/dsBaseClient: DataSHIELD Client Functions

Fits Linear Mixed-Effect model via Study-Level Meta-Analysis

Description

ds.lmerSLMA fits a Linear Mixed-Effects Model (lme) - can include both fixed and random-effects - on data from one or multiple sources with pooling via SLMA (Study-Level Meta-Analysis)

Usage

ds.lmerSLMA(
  formula = NULL,
  offset = NULL,
  weights = NULL,
  combine.with.metafor = TRUE,
  dataName = NULL,
  checks = FALSE,
  datasources = NULL,
  REML = TRUE,
  control_type = NULL,
  control_value = NULL,
  optimizer = NULL,
  verbose = 0,
  notify.of.progress = FALSE,
  assign = FALSE,
  newobj = NULL
)

Arguments

formula	an object of class formula describing the model to be fitted. For more information see Details.
offset	a character string specifying the name of a variable to be used as an offset.
weights	a character string specifying the name of a variable containing prior regression weights for the fitting process.
combine.with.metafor	logical. If TRUE the estimates and standard errors for each regression coefficient are pooled across studies using random-effects meta-analysis under maximum likelihood (ML), restricted maximum likelihood (REML) or fixed-effects meta-analysis (FE). Default TRUE.
dataName	a character string specifying the name of an (optional) data frame that contains all of the variables in the LME formula. For more information see Details.
checks	logical. If TRUE ds.lmerSLMA checks the structural integrity of the model. Default FALSE. For more information see Details.
datasources	a list of DSConnection-class objects obtained after login. If the datasources argument is not specified the default set of connections will be used: see datashield.connections_default.
REML	logical. If TRUE the REstricted Maximum Likelihood (REML) is used for parameter optimization. If FALSE the parameters are optimized using standard ML (maximum likelihood). Default TRUE. For more information see Details.
control_type	an optional character string vector specifying the nature of a parameter (or parameters) to be modified in the convergence control options which can be viewed or modified via the lmerControl function of the package lme4. For more information see Details.
control_value	numeric representing the new value which you want to allocate the control parameter corresponding to the control-type. For more information see Details.
optimizer	specifies the parameter optimizer that lmer should use. For more information see Details.
verbose	an integer value. If verbose > 0 the output is generated during the optimization of the parameter estimates. If verbose > 1 the output is generated during the individual penalized iteratively reweighted least squares (PIRLS) steps. Default verbose value is 0 which means no additional output.
notify.of.progress	specifies if console output should be produced to indicate progress. Default FALSE.
assign	a logical, indicates whether the function will call a second server-side function (an assign) in order to save the regression outcomes (i.e. a lmerMod object) on each server. Default FALSE.
newobj	a character string specifying the name of the object to which the lmerMod object representing the model fit on the serverside in each study is to be written. This argument is used only when the argument assign is set to TRUE. If no <newobj> argument is specified, the output object defaults to "new.lmer.obj".

Details

ds.lmerSLMA fits a Linear Mixed Effects Model (lme) - can include both fixed and random effects - on data from single or multiple sources.

This function is similar to lmer function from lme4 package in native R.

When there are multiple data sources, the LME is fitted to convergence in each data source independently. The estimates and standard errors returned to the client-side which enable cross-study pooling using Study-Level Meta-Analysis (SLMA). The SLMA used by default metafor package but as the SLMA occurs on the client-side (a standard R environment), the user can choose any approach to meta-analysis. Additional information about fitting LMEs using the lmer function can be obtained using R help for lmer and the lme4 package.

In formula most shortcut notation allowed by lmer() function is also allowed by ds.lmerSLMA. Many LMEs can be fitted very simply using a formula like:

y ~ a + b + (1 | c)

which simply means fit an LME with y as the outcome variable with a and b as fixed effects, and c as a random effect or grouping factor.

It is also possible to fit models with random slopes by specifying a model such as

y ~ a + b + (1 + b | c)

where the effect of b can vary randomly between groups defined by c. Implicit nesting can be specified with formulae such as y ~ a + b + (1 | c / d) or y ~ a + b + (1 | c) + (1 | c : d).

The dataName argument avoids you having to specify the name of the data frame in front of each covariate in the formula. For example, if the data frame is called DataFrame you avoid having to write: DataFrame\$y ~ DataFrame\$a + DataFrame\$b + (1 | DataFrame\$c).

The checks argument verifies that the variables in the model are all defined (exist) on the server-site at every study and that they have the correct characteristics required to fit the model. It is suggested to make checks argument TRUE if an unexplained problem in the model fit is encountered because the running process takes several minutes.

REML can help to mitigate bias associated with the fixed-effects. See help on the lmer() function for more details.

In control_type at present only one such parameter can be modified, namely the tolerance of the convergence criterion to the gradient of the log-likelihood at the maximum likelihood achieved. We have enabled this because our practical experience suggests that in situations where the model looks to have converged with sensible parameter values but formal convergence is not being declared if we allow the model to be more tolerant to a non-zero gradient the same parameter values are obtained but formal convergence is declared. The default value for the check.conv.grad is 0.002.

control_value At present (see control_type) the only parameter this can be is the convergence tolerance check.conv.grad. In general, models will be identified as having converged more readily if the value set for check.conv.grad is increased from its default (0.002). Please note that the risk of doing this is that the model is also more likely to be declared as having converged at a local maximum that is not the global maximum likelihood. This will not generally be a problem if the likelihood surface is well behaved but if you have a problem with convergence you might usefully compare all the parameter estimates and standard errors obtained using the default tolerance (0.002) even though that has not formally converged with those obtained after convergence using the higher tolerance.

The optimizer argument is built in but it won't do anything because there is only one standard optimizer available for lmer - this is the nloptwrap optimizer. If users wish to apply a different optimizer - potentially one they have developed themselves - the development team can activate this argument so alternatives can be specified.

Server function called: lmerSLMADS2

Value

Many of the elements of the output list returned by ds.lmerSLMA are equivalent to those returned by the lmer() function in native R. However, potentially disclosive elements such as individual-level residuals and linear predictor values are blocked. In this case, only non-disclosive elements are returned from each study separately.

The list of elements returned by ds.lmerSLMA is mentioned below:

ds.lmerSLMA returns a list of elements mentioned below separately for each study.

coefficients: a matrix with 5 columns:

First

: the names of all of the regression parameters (coefficients) in the model

second

: the estimated values

third

: corresponding standard errors of the estimated values

fourth

: the ratio of estimate/standard error

fifth

: the p-value treating that as a standardised normal deviate

CorrMatrix: the correlation matrix of parameter estimates.

VarCovMatrix: the variance-covariance matrix of parameter estimates.

weights: the vector (if any) holding regression weights.

offset: the vector (if any) holding an offset.

cov.scaled: equivalent to VarCovMatrix.

Nmissing: the number of missing observations in the given study.

Nvalid: the number of valid (non-missing) observations in the given study.

Ntotal: the total number of observations in the given study (Nvalid + Nmissing).

data: equivalent to input parameter dataName (above).

call: summary of key elements of the call to fit the model.

There are a small number of more esoteric items of the information returned by ds.lmerSLMA. Additional information about these can be found in the help file for the lmer() function in the lme4 package.

Once the study-specific output has been returned, the function returns several elements relating to the pooling of estimates across studies via study-level meta-analysis. These are as follows:

input.beta.matrix.for.SLMA: a matrix containing the vector of coefficient estimates from each study.

input.se.matrix.for.SLMA: a matrix containing the vector of standard error estimates for coefficients from each study.

SLMA.pooled.estimates: a matrix containing pooled estimates for each regression coefficient across all studies with pooling under SLMA via random-effects meta-analysis under maximum likelihood (ML), restricted maximum likelihood (REML) or via fixed-effects meta-analysis (FE).

convergence.error.message: reports for each study whether the model converged. If it did not some information about the reason for this is reported.

Author(s)

DataSHIELD Development Team

Examples

## Not run: 

 ## Version 6, for version 5 see Wiki
  # Connecting to the Opal servers
  
  require('DSI')
  require('DSOpal')
  require('dsBaseClient')
  
  builder <- DSI::newDSLoginBuilder()
  builder$append(server = "study1", 
                 url = "http://192.168.56.100:8080/", 
                 user = "administrator", password = "datashield_test&", 
                 table = "CLUSTER.CLUSTER_SLO1", driver = "OpalDriver")
  builder$append(server = "study2", 
                 url = "http://192.168.56.100:8080/", 
                 user = "administrator", password = "datashield_test&", 
                 table = "CLUSTER.CLUSTER_SLO2", driver = "OpalDriver")
  builder$append(server = "study3",
                 url = "http://192.168.56.100:8080/", 
                 user = "administrator", password = "datashield_test&", 
                 table = "CLUSTER.CLUSTER_SLO3", driver = "OpalDriver")
  logindata <- builder$build()
  
   #Log onto the remote Opal training servers
   connections <- DSI::datashield.login(logins = logindata, assign = TRUE, symbol = "D")
               
  # Select all rows without missing values
  ds.completeCases(x1 = "D", newobj = "D.comp", datasources = connections)
 
  # Fit the lmer
  
  ds.lmerSLMA(formula = "BMI ~ incid_rate + diabetes + (1 | Male)",
               dataName = "D.comp",
               datasources = connections)
  
  # Clear the Datashield R sessions and logout
  datashield.logout(connections) 
  
## End(Not run)

datashield/dsBaseClient documentation built on Nov. 16, 2024, 2:07 p.m.