coefficients in opposite signs compared to survreg

I see conflicting results between survival and flexsurv. Is there a reason for this? Below is a reproducible example.

From the data, I know that the output from survival is the correct one and flexsurv is also correct, but it's in the opposite sign.

library(survival)
#> Warning: package 'survival' was built under R version 4.3.3
library(flexsurv)
#> Warning: package 'flexsurv' was built under R version 4.3.3
library(haven)
df <- read_dta("http://web1.sph.emory.edu/dkleinb/allDatasets/surv2datasets/anderson.dta")

mod1 <- flexsurv::flexsurvreg(Surv(survt, status) ~ rx, data = df, dist = "exponential")
mod2 <- survival::survreg(Surv(survt, status) ~ rx, data = df, dist = "exponential")

mod1
#> Call:
#> flexsurv::flexsurvreg(formula = Surv(survt, status) ~ rx, data = df, 
#>     dist = "exponential")
#> 
#> Estimates: 
#>       data mean  est       L95%      U95%      se        exp(est)  L95%    
#> rate        NA    0.02507   0.01304   0.04818   0.00836        NA        NA
#> rx     0.50000    1.52661   0.74575   2.30748   0.39841   4.60256   2.10801
#>       U95%    
#> rate        NA
#> rx    10.04909
#> 
#> N = 42,  Events: 30,  Censored: 12
#> Total time at risk: 541
#> Log-likelihood = -108.524, df = 2
#> AIC = 221.0481
mod2
#> Call:
#> survival::survreg(formula = Surv(survt, status) ~ rx, data = df, 
#>     dist = "exponential")
#> 
#> Coefficients:
#> (Intercept)          rx 
#>    3.686098   -1.526614 
#> 
#> Scale fixed at 1 
#> 
#> Loglik(model)= -108.5   Loglik(intercept only)= -116.8
#>  Chisq= 16.49 on 1 degrees of freedom, p= 4.9e-05 
#> n= 42

^{Created on 2024-03-24 with reprex v2.1.0}

Session info

``` r sessioninfo::session_info() #> ─ Session info ─────────────────────────────────────────────────────────────── #> setting value #> version R version 4.3.2 (2023-10-31 ucrt) #> os Windows 11 x64 (build 22631) #> system x86_64, mingw32 #> ui RTerm #> language (EN) #> collate English_United States.utf8 #> ctype English_United States.utf8 #> tz America/Chicago #> date 2024-03-24 #> pandoc 3.1.1 @ C:/Program Files/RStudio/resources/app/bin/quarto/bin/tools/ (via rmarkdown) #> #> ─ Packages ─────────────────────────────────────────────────────────────────── #> package * version date (UTC) lib source #> cli 3.6.2 2023-12-11 [1] CRAN (R 4.3.2) #> colorspace 2.1-0 2023-01-23 [1] CRAN (R 4.3.2) #> curl 5.2.1 2024-03-01 [1] CRAN (R 4.3.3) #> data.table 1.15.2 2024-02-29 [1] CRAN (R 4.3.3) #> deSolve 1.40 2023-11-27 [1] CRAN (R 4.3.3) #> digest 0.6.35 2024-03-11 [1] CRAN (R 4.3.3) #> dplyr 1.1.4 2023-11-17 [1] CRAN (R 4.3.2) #> evaluate 0.23 2023-11-01 [1] CRAN (R 4.3.2) #> fansi 1.0.6 2023-12-08 [1] CRAN (R 4.3.2) #> fastmap 1.1.1 2023-02-24 [1] CRAN (R 4.3.2) #> flexsurv * 2.2.2 2023-02-01 [1] CRAN (R 4.3.3) #> forcats 1.0.0 2023-01-29 [1] CRAN (R 4.3.2) #> fs 1.6.3 2023-07-20 [1] CRAN (R 4.3.2) #> generics 0.1.3 2022-07-05 [1] CRAN (R 4.3.2) #> ggplot2 3.5.0 2024-02-23 [1] CRAN (R 4.3.3) #> glue 1.7.0 2024-01-09 [1] CRAN (R 4.3.3) #> gtable 0.3.4 2023-08-21 [1] CRAN (R 4.3.2) #> haven * 2.5.4 2023-11-30 [1] CRAN (R 4.3.2) #> hms 1.1.3 2023-03-21 [1] CRAN (R 4.3.2) #> htmltools 0.5.7 2023-11-03 [1] CRAN (R 4.3.2) #> knitr 1.45 2023-10-30 [1] CRAN (R 4.3.2) #> lattice 0.22-6 2024-03-20 [2] CRAN (R 4.3.2) #> lifecycle 1.0.4 2023-11-07 [1] CRAN (R 4.3.2) #> magrittr 2.0.3 2022-03-30 [1] CRAN (R 4.3.2) #> Matrix 1.6-5 2024-01-11 [2] CRAN (R 4.3.3) #> mstate 0.3.2 2021-11-08 [1] CRAN (R 4.3.3) #> muhaz 1.2.6.4 2021-04-21 [1] CRAN (R 4.3.3) #> munsell 0.5.0 2018-06-12 [1] CRAN (R 4.3.2) #> mvtnorm 1.2-4 2023-11-27 [2] CRAN (R 4.3.2) #> numDeriv 2016.8-1.1 2019-06-06 [2] CRAN (R 4.3.1) #> pillar 1.9.0 2023-03-22 [1] CRAN (R 4.3.2) #> pkgconfig 2.0.3 2019-09-22 [1] CRAN (R 4.3.2) #> purrr 1.0.2 2023-08-10 [1] CRAN (R 4.3.2) #> quadprog 1.5-8 2019-11-20 [1] CRAN (R 4.3.1) #> R.cache 0.16.0 2022-07-21 [1] CRAN (R 4.3.2) #> R.methodsS3 1.8.2 2022-06-13 [1] CRAN (R 4.3.1) #> R.oo 1.26.0 2024-01-24 [1] CRAN (R 4.3.2) #> R.utils 2.12.3 2023-11-18 [1] CRAN (R 4.3.2) #> R6 2.5.1 2021-08-19 [1] CRAN (R 4.3.2) #> Rcpp 1.0.12 2024-01-09 [1] CRAN (R 4.3.3) #> readr 2.1.5 2024-01-10 [1] CRAN (R 4.3.3) #> reprex 2.1.0 2024-01-11 [1] CRAN (R 4.3.3) #> rlang 1.1.3 2024-01-10 [1] CRAN (R 4.3.3) #> rmarkdown 2.26 2024-03-05 [1] CRAN (R 4.3.3) #> rstudioapi 0.16.0 2024-03-24 [1] CRAN (R 4.3.2) #> scales 1.3.0 2023-11-28 [1] CRAN (R 4.3.2) #> sessioninfo 1.2.2 2021-12-06 [2] CRAN (R 4.3.2) #> statmod 1.5.0 2023-01-06 [1] CRAN (R 4.3.3) #> styler 1.10.2 2023-08-29 [1] CRAN (R 4.3.2) #> survival * 3.5-8 2024-02-14 [2] CRAN (R 4.3.3) #> tibble 3.2.1 2023-03-20 [1] CRAN (R 4.3.2) #> tidyr 1.3.1 2024-01-24 [1] CRAN (R 4.3.3) #> tidyselect 1.2.1 2024-03-11 [1] CRAN (R 4.3.3) #> tzdb 0.4.0 2023-05-12 [1] CRAN (R 4.3.2) #> utf8 1.2.4 2023-10-22 [1] CRAN (R 4.3.2) #> vctrs 0.6.5 2023-12-01 [1] CRAN (R 4.3.2) #> withr 3.0.0 2024-01-16 [1] CRAN (R 4.3.3) #> xfun 0.42 2024-02-08 [1] CRAN (R 4.3.3) #> yaml 2.3.8 2023-12-11 [1] CRAN (R 4.3.2) #> #> [1] C:/Users/aabdel51/AppData/Local/R/win-library/4.3 #> [2] C:/Users/aabdel51/AppData/Local/Programs/R/R-4.3.2/library #> #> ────────────────────────────────────────────────────────────────────────────── ```

chjackson / flexsurv

coefficients in opposite signs compared to survreg #184