Confidence intervals for hurdle or zero inflated mixed models - r

Question

I want to calculate CI in mixed models, zero inflated negative binomial and hurdle model. My code for hurdle model looks like this (x1, x2 continuous, x3 categorical):
m1 <- glmmTMB(count~x1+x2+x3+(1|year/class),
data = bd, zi = ~x2+x3+(1|year/class), family = truncated_nbinom2,
)
I used confint, and I got these results:
ci <- confint(m1,parm="beta_")
ci
2.5 % 97.5 % Estimate
cond.(Intercept) 1.816255e-01 0.448860094 0.285524861
cond.x1 9.045278e-01 0.972083366 0.937697401
cond.x2 1.505770e+01 26.817439186 20.094998772
cond.x3high 1.190972e+00 1.492335046 1.333164894
cond.x3low 1.028147e+00 1.215828654 1.118056377
cond.x3reg 1.135515e+00 1.385833853 1.254445909
class:year.cond.Std.Dev.(Intercept)2.256324e+00 2.662976154 2.441845815
year.cond.Std.Dev.(Intercept) 1.051889e+00 1.523719169 1.157153015
zi.(Intercept) 1.234418e-04 0.001309705 0.000402085
zi.x2 2.868578e-02 0.166378014 0.069084606
zi.x3high 8.972025e-01 1.805832900 1.272869874
Am I calculating the intervals correctly? Why is there only one category in x3 for zi?
If possible, I would also like to know if it's possible to plot these CIs.
Thanks!
Data looks like this:
class id year count x1 x2 x3
956 5 3002 2002 3 15.6 47.9 high
957 5 4004 2002 3 14.3 47.9 low
958 5 6021 2002 3 14.2 47.9 high
959 4 2030 2002 3 10.5 46.3 high
960 4 2031 2002 3 15.3 46.3 high
961 4 2034 2002 3 15.2 46.3 reg
with x1 and x2 continuous, x3 three level categorical variable (factor)
Summary of the model:
summary(m1)
'giveCsparse' has been deprecated; setting 'repr = "T"' for you'giveCsparse' has been deprecated; setting 'repr = "T"' for you'giveCsparse' has been deprecated; setting 'repr = "T"' for you
Family: truncated_nbinom2 ( log )
Formula: count ~ x1 + x2 + x3 + (1 | year/class)
Zero inflation: ~x2 + x3 + (1 | year/class)
Data: bd
AIC BIC logLik deviance df.resid
37359.7 37479.7 -18663.8 37327.7 13323
Random effects:
Conditional model:
Groups Name Variance Std.Dev.
class:year(Intercept) 0.79701 0.8928
year (Intercept) 0.02131 0.1460
Number of obs: 13339, groups: class:year, 345; year, 15
Zero-inflation model:
Groups Name Variance Std.Dev.
dpto:year (Intercept) 1.024e+02 1.012e+01
year (Intercept) 7.842e-07 8.856e-04
Number of obs: 13339, groups: class:year, 345; year, 15
Overdispersion parameter for truncated_nbinom2 family (): 1.02
Conditional model:
Estimate Std. Error z value Pr(>|z|)
(Intercept) -1.25343 0.23081 -5.431 5.62e-08 ***
x1 -0.06433 0.01837 -3.501 0.000464 ***
x2 3.00047 0.14724 20.378 < 2e-16 ***
x3high 0.28756 0.05755 4.997 5.82e-07 ***
x3low 0.11159 0.04277 2.609 0.009083 **
x3reg 0.22669 0.05082 4.461 8.17e-06 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Zero-inflation model:
Estimate Std. Error z value Pr(>|z|)
(Intercept) -7.8188 0.6025 -12.977 < 2e-16 ***
x2 -2.6724 0.4484 -5.959 2.53e-09 ***
x3high 0.2413 0.1784 1.352 0.17635
x3low -0.1325 0.1134 -1.169 0.24258
x3reg -0.3806 0.1436 -2.651 0.00802 **
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
CI with broom.mixed
> broom.mixed::tidy(m1, effects="fixed", conf.int=TRUE)
# A tibble: 12 x 9
effect component term estimate std.error statistic p.value conf.low conf.high
<chr> <chr> <chr> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
1 fixed cond (Intercept) -1.25 0.231 -5.43 5.62e- 8 -1.71 -0.801
2 fixed cond x1 -0.0643 0.0184 -3.50 4.64e- 4 -0.100 -0.0283
3 fixed cond x2 3.00 0.147 20.4 2.60e-92 2.71 3.29
4 fixed cond x3high 0.288 0.0575 5.00 5.82e- 7 0.175 0.400
5 fixed cond x3low 0.112 0.0428 2.61 9.08e- 3 0.0278 0.195
6 fixed cond x3reg 0.227 0.0508 4.46 8.17e- 6 0.127 0.326
7 fixed zi (Intercept) -9.88 1.32 -7.49 7.04e-14 -12.5 -7.30
8 fixed zi x1 0.214 0.120 1.79 7.38e- 2 -0.0206 0.448
9 fixed zi x2 -2.69 0.449 -6.00 2.01e- 9 -3.57 -1.81
10 fixed zi x3high 0.232 0.178 1.30 1.93e- 1 -0.117 0.582
11 fixed zi x3low -0.135 0.113 -1.19 2.36e- 1 -0.357 0.0878
12 fixed zi x4reg -0.382 0.144 -2.66 7.74e- 3 -0.664 -0.101

Answer 1

tl;dr as far as I can tell this is a bug in confint.glmmTMB (and probably in the internal function glmmTMB:::getParms). In the meantime, broom.mixed::tidy(m1, effects="fixed") should do what you want. (There's now a fix in progress in the development version on GitHub, should make it to CRAN sometime? soon ...)
Reproducible example:
set up data
set.seed(101)
n <- 1e3
bd <- data.frame(
year=factor(sample(2002:2018, size=n, replace=TRUE)),
class=factor(sample(1:20, size=n, replace=TRUE)),
x1 = rnorm(n),
x2 = rnorm(n),
x3 = factor(sample(c("low","reg","high"), size=n, replace=TRUE),
levels=c("low","reg","high")),
count = rnbinom(n, mu = 3, size=1))
fit
library(glmmTMB)
m1 <- glmmTMB(count~x1+x2+x3+(1|year/class),
data = bd, zi = ~x2+x3+(1|year/class), family = truncated_nbinom2,
)
confidence intervals
confint(m1, "beta_") ## wrong/ incomplete
broom.mixed::tidy(m1, effects="fixed", conf.int=TRUE) ## correct
You may want to think about which kind of confidence intervals you want:
Wald CIs (default) are much faster to compute and are generally OK as long as (1) your data set is large and (2) you aren't estimating any parameters on the log/logit scale that are near the boundaries
likelihood profile CIs are more accurate but much slower