Comparison with other packages

James T. Thorson and Wouter van der Bijl

library(phylosem)

phylosem is an R package for fitting phylogenetic structural equation models (PSEMs). The package generalizes features in existing R packages:

In model configurations that can be fitted by both phylosem and these other packages, we have confirmed that results are nearly identical or otherwise identified reasons that results differ.

phylosem involves a simple user-interface that specifies the SEM using notation from package sem and the phylogenetic tree using package ape. It allows uers to specify common models for the covariance including:

Output can be coerced to standard formats so that phylosem can use plotting and summary functions form other packages. Available output formats include:

Below, we specifically highlight the syntax, runtime, and output resulting from phylosem and other packages.

Comparison with phylolm

We first compare syntax and run-times using simulated data against phylolm. This confirms that runtimes from phylosem are within an order of magnitude and that results are nearly identical for BM, OU, delta, and kappa models.

# Settings
Ntree = 100
sd_x = 0.3
sd_y = 0.3
b0_x = 1
b0_y = 0
b_xy = 1

# Simulate tree
set.seed(1)
tree = ape::rtree(n=Ntree)

# Simulate data
x = b0_x + sd_x * phylolm::rTrait(n = 1, phy=tree)
ybar = b0_y + b_xy*x
y_normal = ybar + sd_y * phylolm::rTrait(n = 1, phy=tree)

# Construct, re-order, and reduce data
Data = data.frame(x=x,y=y_normal)[]

# Compare using BM model
start_time = Sys.time()
plm_bm = phylolm::phylolm(y ~ 1 + x, data=Data, phy=tree, model="BM" )
Sys.time() - start_time
#> Time difference of 0.008763075 secs
knitr::kable(summary(plm_bm)$coefficients, digits=3)
Estimate StdErr t.value p.value
(Intercept) -0.371 0.214 -1.734 0.086
x 1.117 0.101 11.053 0.000

start_time = Sys.time()
psem_bm = phylosem( sem = "x -> y, p",
          data = Data,
          tree = tree,
          control = phylosem_control(quiet = TRUE) )
Sys.time() - start_time
#> Time difference of 0.1372821 secs
knitr::kable(summary(psem_bm)$coefficients, digits=3)
Path VarName Estimate StdErr t.value p.value
NA Intercept_x 1.087 0.183 5.945 0.000
NA Intercept_y -0.371 0.213 1.743 0.081
x -> y p 1.117 0.101 11.109 0.000
x <-> x V[x] 0.315 0.022 14.072 0.000
y <-> y V[y] 0.315 0.022 14.072 0.000

# Compare using OU
start_time = Sys.time()
plm_ou = phylolm::phylolm(y ~ 1 + x, data=Data, phy=tree, model="OUrandomRoot" )
Sys.time() - start_time
#> Time difference of 0.01075983 secs

start_time = Sys.time()
psem_ou = phylosem( sem = "x -> y, p",
          data = Data,
          tree = tree,
          estimate_ou = TRUE,
          control = phylosem_control(quiet = TRUE) )
Sys.time() - start_time
#> Time difference of 0.1098459 secs

knitr::kable(summary(psem_ou)$coefficients, digits=3)
Path VarName Estimate StdErr t.value p.value
NA Intercept_x 1.028 0.208 4.946 0.000
NA Intercept_y -0.274 0.235 1.165 0.244
x -> y p 1.099 0.101 10.887 0.000
x <-> x V[x] 0.332 0.026 12.712 0.000
y <-> y V[y] 0.332 0.026 12.860 0.000
knitr::kable(summary(plm_ou)$coefficients, digits=3)
Estimate StdErr t.value p.value
(Intercept) -0.781 0.389 -2.006 0.048
x 1.095 0.101 10.850 0.000
knitr::kable(c( "phylolm_alpha"=plm_ou$optpar, 
                "phylosem_alpha"=exp(psem_ou$parhat$lnalpha) ), digits=3)
x
phylolm_alpha 0.120
phylosem_alpha 0.105

# Compare using Pagel's lambda
start_time = Sys.time()
plm_lambda = phylolm::phylolm(y ~ 1 + x, data=Data, phy=tree, model="lambda" )
Sys.time() - start_time
#> Time difference of 0.01883388 secs

start_time = Sys.time()
psem_lambda = phylosem( sem = "x -> y, p",
          data = Data,
          tree = tree,
          estimate_lambda = TRUE,
          control = phylosem_control(quiet = TRUE) )
Sys.time() - start_time
#> Time difference of 0.08508587 secs

knitr::kable(summary(psem_lambda)$coefficients, digits=3)
Path VarName Estimate StdErr t.value p.value
NA Intercept_x 1.092 0.162 6.740 0.000
NA Intercept_y -0.346 0.200 1.726 0.084
x -> y p 1.092 0.103 10.559 0.000
x <-> x V[x] 0.284 0.025 11.367 0.000
y <-> y V[y] 0.290 0.024 11.897 0.000
knitr::kable(summary(plm_lambda)$coefficients, digits=3)
Estimate StdErr t.value p.value
(Intercept) -0.356 0.207 -1.718 0.089
x 1.102 0.103 10.744 0.000
knitr::kable(c( "phylolm_lambda"=plm_lambda$optpar, 
                "phylosem_lambda"=plogis(psem_lambda$parhat$logitlambda) ), digits=3)
x
phylolm_lambda 0.980
phylosem_lambda 0.957

# Compare using Pagel's kappa
start_time = Sys.time()
plm_kappa = phylolm::phylolm(y ~ 1 + x, data=Data, phy=tree, model="kappa", lower.bound = 0, upper.bound = 3 )
Sys.time() - start_time
#> Time difference of 0.004974842 secs

start_time = Sys.time()
psem_kappa = phylosem( sem = "x -> y, p",
          data = Data,
          tree = tree,
          estimate_kappa = TRUE,
          control = phylosem_control(quiet = TRUE) )
Sys.time() - start_time
#> Time difference of 0.09007502 secs

knitr::kable(summary(psem_kappa)$coefficients, digits=3)
Path VarName Estimate StdErr t.value p.value
NA Intercept_x 1.078 0.186 5.783 0.000
NA Intercept_y -0.368 0.216 1.705 0.088
x -> y p 1.113 0.101 11.025 0.000
x <-> x V[x] 0.299 0.029 10.183 0.000
y <-> y V[y] 0.300 0.029 10.343 0.000
knitr::kable(summary(plm_kappa)$coefficients, digits=3)
Estimate StdErr t.value p.value
(Intercept) -0.370 0.216 -1.716 0.089
x 1.115 0.101 11.015 0.000
knitr::kable(c( "phylolm_kappa"=plm_kappa$optpar, 
                "phylosem_kappa"=exp(psem_kappa$parhat$lnkappa) ), digits=3)
x
phylolm_kappa 0.930
phylosem_kappa 0.857

Generalized linear models

We also compare results among software for fitting phylogenetic generalized linear models (PGLM).

Poisson-distributed response

First, we specifically explore a Poisson-distributed PGLM, comparing phylosem against phylolm::phyloglm (which uses Generalized Estimating Equations) and phyr::pglmm_compare (which uses maximum likelihood).

# Settings
Ntree = 100
sd_x = 0.3
sd_y = 0.3
b0_x = 1
b0_y = 0
b_xy = 1

# Simulate tree
set.seed(1)
tree = ape::rtree(n=Ntree)

# Simulate data
x = b0_x + sd_x * phylolm::rTrait(n = 1, phy=tree)
ybar = b0_y + b_xy*x
y_normal = ybar + sd_y * phylolm::rTrait(n = 1, phy=tree)
y_pois = rpois( n=Ntree, lambda=exp(y_normal) )

# Construct, re-order, and reduce data
Data = data.frame(x=x,y=y_pois)

# Compare using phylolm::phyloglm
pglm = phylolm::phyloglm(y ~ 1 + x, data=Data, phy=tree, method="poisson_GEE" )
knitr::kable(summary(pglm)$coefficients, digits=3)
Estimate StdErr z.value p.value
(Intercept) -1.098 0.633 -1.736 0.083
x 1.314 0.247 5.320 0.000

#
pglmm = phyr::pglmm_compare(
  y ~ 1 + x,
  family = "poisson",
  data = Data,
  phy = tree )
knitr::kable(summary(pglmm), digits=3)
#> Generalized linear mixed model for poisson data fit by restricted maximum likelihood
#> 
#> Call:y ~ 1 + x
#> 
#> logLik    AIC    BIC 
#> -173.4  354.7  360.6 
#> 
#> Phylogenetic random effects variance (s2):
#>    Variance Std.Dev
#> s2  0.05511  0.2348
#> 
#> Fixed effects:
#>                Value Std.Error  Zscore    Pvalue    
#> (Intercept) -0.57009   0.30469 -1.8710   0.06134 .  
#> x            1.18137   0.19807  5.9645 2.454e-09 ***
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

#
pgsem = phylosem( sem = "x -> y, p",
          data = Data,
          family = c("fixed","poisson"),
          tree = tree,
          control = phylosem_control(quiet = TRUE) )
knitr::kable(summary(pgsem)$coefficients, digits=3)
Path VarName Estimate StdErr t.value p.value
NA Intercept_x 1.087 0.183 5.945 0.000
NA Intercept_y -0.581 0.305 1.904 0.057
x -> y p 1.190 0.199 5.971 0.000
x <-> x V[x] 0.315 0.022 14.072 0.000
y <-> y V[y] 0.232 0.054 4.310 0.000

We also compare results against brms (which fits a Bayesian hierarchical model), although we load results from compiled run of brms to avoid users having to install STAN to run vignettes for phylosem:

# Comare using Bayesian implementation in brms
library(brms)
Amat <- ape::vcv.phylo(tree)
Data$tips <- rownames(Data)
mcmc <- brm(
  y ~ 1 + x + (1 | gr(tips, cov = A)),
  data = Data, data2 = list(A = Amat),
  family = 'poisson',
  cores = 4
)
knitr::kable(fixef(mcmc), digits = 3)

# Plot them together
library(ggplot2)
pdat <- rbind.data.frame(
  coef(summary(pglm))[, 1:2],
  data.frame(Estimate = pglmm$B, StdErr = pglmm$B.se),
  setNames(as.data.frame(fixef(mcmc))[1:2], c('Estimate', 'StdErr')),
  setNames(summary(pgsem)$coefficients[2:3, 3:4], c('Estimate', 'StdErr'))
)
pdat$Param <- rep(c('Intercept', 'Slope'), 4)
pdat$Method <- rep( c('phylolm::phyloglm', 'phyr::pglmm_compare',
                     'brms::brm', 'phylosem::phylosem'), each = 2)
figure = ggplot(pdat, aes(
  x = Estimate, xmin = Estimate - StdErr,
  xmax = Estimate + StdErr, y = Param, color = Method
)) +
  geom_pointrange(position = position_dodge(width = 0.6)) +
  theme_classic() +
  theme(panel.grid.major.x = element_line(), panel.grid.minor.x = element_line())

In this instance (and in others we have explored), results from phylolm::phyloglm are generally different while those from phylosem, phyr::pglmm_compare, and brms are close but not quite identical.

Binomial regression

We also compare results for a Bernoulli-distributed response using PGLM. We again compare phylosem against phyr::pglmm_compare, and do not explore threshold models which we expect to give different results due differences in assumptions about how latent variables affect measurements.

# Settings
Ntree = 100
sd_x = 0.3
sd_y = 0.3
b0_x = 1
b0_y = 0
b_xy = 1

# Simulate tree
set.seed(1)
tree = ape::rtree(n=Ntree)

# Simulate data
x = b0_x + sd_x * phylolm::rTrait(n = 1, phy=tree)
ybar = b0_y + b_xy*x
y_normal = ybar + sd_y * phylolm::rTrait(n = 1, phy=tree)
y_binom = rbinom( n=Ntree, size=1, prob=plogis(y_normal) )

# Construct, re-order, and reduce data
Data = data.frame(x=x,y=y_binom)

#
pglmm = phyr::pglmm_compare(
  y ~ 1 + x,
  family = "binomial",
  data = Data,
  phy = tree )
knitr::kable(summary(pglmm), digits=3)
#> Generalized linear mixed model for binomial data fit by restricted maximum likelihood
#> 
#> Call:y ~ 1 + x
#> 
#> logLik    AIC    BIC 
#> -63.74 135.47 141.32 
#> 
#> Phylogenetic random effects variance (s2):
#>    Variance Std.Dev
#> s2   0.1076   0.328
#> 
#> Fixed effects:
#>               Value Std.Error Zscore Pvalue
#> (Intercept) 0.23179   0.60507 0.3831 0.7017
#> x           0.44548   0.45708 0.9746 0.3297

#
pgsem = phylosem( sem = "x -> y, p",
          data = Data,
          family = c("fixed","binomial"),
          tree = tree,
          control = phylosem_control(quiet = TRUE) )
knitr::kable(summary(pgsem)$coefficients, digits=3)
Path VarName Estimate StdErr t.value p.value
NA Intercept_x 1.087 0.183 5.945 0.000
NA Intercept_y 0.204 0.589 0.346 0.730
x -> y p 0.458 0.468 0.977 0.328
x <-> x V[x] -0.315 0.022 14.072 0.000
y <-> y V[y] 0.290 0.284 1.020 0.308

In this instance, phylosem and phyr::pglmm_compare give similar estimates and standard errors for the slope term.

Summary of PGLM results

Based on these two comparisons, we conclude that phylosem provides an interface for maximum-likelihood estimate of phylogenetic generalized linear models (PGLM), and extends this class to include mixed data (i.e., a combination of different measurement types), missing data, and non-recursive structural linkages. However, we also encourage further cross-testing of different software for fitting phylogenetic generalized linear models.

Compare with phylopath

We next compare with a single run of phylopath. This again confirms that runtimes are within an order of magnitude and results are identical for standardized or unstandardized coefficients.

library(phylopath)
library(phylosem)

# make copy of data that's rescaled
rhino_scaled = rhino
  rhino_scaled[,c("BM","NL","LS","DD","RS")] = scale(rhino_scaled[,c("BM","NL","LS","DD","RS")])

# Fit and plot using phylopath
dag <- DAG(RS ~ DD, LS ~ BM, NL ~ BM, DD ~ NL)
start_time = Sys.time()
result <- est_DAG( DAG = dag,
                    data = rhino,
                    tree = rhino_tree,
                    model = "BM",
                    measurement_error = FALSE )
Sys.time() - start_time
#> Time difference of 0.008988142 secs
plot(result)


# Fit and plot using phylosem
model = "
  DD -> RS, p1
  BM -> LS, p2
  BM -> NL, p3
  NL -> DD, p4
"
start_time = Sys.time()
psem = phylosem( sem = model,
          data = rhino_scaled[,c("BM","NL","DD","RS","LS")],
          tree = rhino_tree,
          control = phylosem_control(quiet = TRUE) )
Sys.time() - start_time
#> Time difference of 0.1900501 secs
plot( as_fitted_DAG(psem) )

Comparison with sem

We next compare syntax and runtime against R-package sem. This confirms that runtimes are within an order of magnitude when specifying a star-phylogeny in phylosem to match the assumed structure in sem

library(sem)
library(TreeTools)

# Simulation parameters
n_obs = 50
# Intercepts
a1 = 1
a2 = 2
a3 = 3
a4 = 4
# Slopes
b12 = 0.3
b23 = 0
b34 = 0.3
# Standard deviations
s1 = 0.1
s2 = 0.2
s3 = 0.3
s4 = 0.4

# Simulate data
E1 = rnorm(n_obs, sd=s1)
E2 = rnorm(n_obs, sd=s2)
E3 = rnorm(n_obs, sd=s3)
E4 = rnorm(n_obs, sd=s4)
Y1 = a1 + E1
Y2 = a2 + b12*Y1 + E2
Y3 = a3 + b23*Y2 + E3
Y4 = a4 + b34*Y3 + E4
Data = data.frame(Y1=Y1, Y2=Y2, Y3=Y3, Y4=Y4)

# Specify path diagram (in this case, using correct structure)
equations = "
  Y2 = b12 * Y1
  Y4 = b34 * Y3
"
model <- specifyEquations(text=equations, exog.variances=TRUE, endog.variances=TRUE)

# Fit using package:sem
start_time = Sys.time()
Sem <- sem(model, data=Data)
Sys.time() - start_time
#> Time difference of 0.01324606 secs

# Specify star phylogeny
tree_null = TreeTools::StarTree(n_obs)
  tree_null$edge.length = rep(1,nrow(tree_null$edge))
  rownames(Data) = tree_null$tip.label

# Fit using phylosem
start_time = Sys.time()
psem = phylosem( data = Data,
          sem = equations,
          tree = tree_null,
          control = phylosem_control(quiet = TRUE) )
Sys.time() - start_time
#> Time difference of 0.03360009 secs

We then compare estimated values for standardized coefficients

x
b12 0.326
b34 0.325
Path Parameter Estimate
Y1 -> Y2 b12 0.345
Y3 -> Y4 b34 0.343

and also compare values for unstandardized coefficients:

x
b12 0.660
b34 0.390
V[Y1] 0.010
V[Y2] 0.038
V[Y3] 0.098
V[Y4] 0.126
Path Parameter Estimate
Y1 -> Y2 b12 0.660
Y3 -> Y4 b34 0.390
Y1 <-> Y1 V[Y1] 0.010
Y2 <-> Y2 V[Y2] 0.038
Y3 <-> Y3 V[Y3] 0.098
Y4 <-> Y4 V[Y4] 0.126

Comparison with Rphylopars

Finally, we compare syntax and runtime against R-package Rphylopars. This confirms that we can impute identical estimates using both packages, when specifying a full-rank covariance in phylosem

We note that phylosem also allows parsimonious representations of the trait covariance via the inputted SEM structure.

library(Rphylopars)

# Format data, within no values for species t1
Data = rhino[,c("BM","NL","DD","RS","LS")]
  rownames(Data) = tree$tip.label
Data['t1',] = NA

# fit using phylopars
start_time = Sys.time()
pars <- phylopars( trait_data = cbind(species=rownames(Data),Data),
                  tree = tree,
                  pheno_error = FALSE,
                  phylo_correlated = TRUE,
                  pheno_correlated = FALSE)
Sys.time() - start_time
#> Time difference of 0.09879303 secs

# Display estimates for missing values
knitr::kable(cbind( "Estimate"=pars$anc_recon["t1",], "Var"=pars$anc_var["t1",] ), digits=3)
Estimate Var
BM 1.266 1.941
NL 1.600 1.856
DD 2.301 1.708
RS 0.431 1.909
LS 1.083 1.347

# fit using phylosem
start_time = Sys.time()
psem = phylosem( data = Data,
                 tree = tree,
                 sem = "",
                 covs = "BM, NL, DD, RS, LS",
                 control = phylosem_control(quiet = TRUE) )
Sys.time() - start_time
#> Time difference of 0.3013921 secs

# Display estimates for missing values
knitr::kable(cbind(
  "Estimate"=as.list(psem$sdrep,"Estimate")$x_vj[ match("t1",tree$tip.label), ],
  "Var"=as.list(psem$sdrep,"Std. Error")$x_vj[ match("t1",tree$tip.label), ]^2
), digits=3)
Estimate Var
1.266 1.941
1.600 1.856
2.301 1.708
0.431 1.910
1.083 1.347