Image credit: Coursera

Risk versus Ratio

Part 2

A maybe not so short summary …

Risk is based on the proportion of persons with disease or outcome of interest expressed as a percentage.

Cumulative Incidence (CI) refers to the occurs of disease in a group studied over time. The disadvantages are:

  1. Everyone has to be followed up for the complete duration of the study
    • Unfortunately, some may die from some other cause or be lost to follow-up, which makes the resulting calculation uncertain.
    • If a person dies, can you be sure that they would not have got the disease if they had lived?
  2. Many conditions can occur more than once
    • If you include them, the incidence proportion could exceed one. While if you accept just first diagnosis, you may underestimate the true burden of disease.

Rate is the number of new cases devided by the total person-time-at-risk for the population.

As risk and CI, incidence rates (IR) also measure the frequency of new cases of the disease in a population. IR take into account the time that each subject remain under investigation and at risk of developing the outcome of interest. Calculate incidences rate, if you have periodic follow-up information on each subject, including not only if they develop the outcome, but also when they developed it.

On the other hand, CI is useful when you want to describe the incidence of disease in a population, but do not have detailed information on each member of the population. For instance, if you want to study the incidence of bladder cancer in Sweden in 2015, but based on the data you can’t take into account when exactly people developed bladder cancer, or if they left the country. If you did have this information, IR would take these factors into account. IR will provide a more accurate estimate of the rate at which bladder cancer develops. It is particularly useful when trying to measure incidence in studies with dynamic populations and in studies with fixed populations with relatively long follow-up time.

Reproducibility

## ─ Session info ───────────────────────────────────────────────────────────────────────────────────────────────────────
##  setting  value                       
##  version  R version 3.5.3 (2019-03-11)
##  os       macOS Mojave 10.14.6        
##  system   x86_64, darwin15.6.0        
##  ui       X11                         
##  language (EN)                        
##  collate  en_US.UTF-8                 
##  ctype    en_US.UTF-8                 
##  tz       Europe/Stockholm            
##  date     2019-11-10                  
## 
## ─ Packages ───────────────────────────────────────────────────────────────────────────────────────────────────────────
##  package       * version    date       lib source                         
##  assertthat      0.2.1      2019-03-21 [1] CRAN (R 3.5.2)                 
##  backports       1.1.5      2019-10-02 [1] CRAN (R 3.5.2)                 
##  BiasedUrn       1.07       2015-12-28 [1] CRAN (R 3.5.0)                 
##  bibtex          0.4.2      2017-06-30 [1] CRAN (R 3.5.0)                 
##  blogdown        0.16       2019-10-01 [1] CRAN (R 3.5.2)                 
##  bookdown        0.14       2019-10-01 [1] CRAN (R 3.5.2)                 
##  callr           3.3.2      2019-09-22 [1] CRAN (R 3.5.2)                 
##  cli             1.1.0      2019-03-19 [1] CRAN (R 3.5.2)                 
##  crayon          1.3.4      2017-09-16 [1] CRAN (R 3.5.0)                 
##  desc            1.2.0      2018-05-01 [1] CRAN (R 3.5.0)                 
##  devtools      * 2.2.1      2019-09-24 [1] CRAN (R 3.5.2)                 
##  digest          0.6.21     2019-09-20 [1] CRAN (R 3.5.2)                 
##  ellipsis        0.3.0      2019-09-20 [1] CRAN (R 3.5.2)                 
##  epiR          * 1.0-4      2019-08-23 [1] CRAN (R 3.5.2)                 
##  evaluate        0.14       2019-05-28 [1] CRAN (R 3.5.2)                 
##  fs              1.3.1      2019-05-06 [1] CRAN (R 3.5.2)                 
##  glue            1.3.1.9000 2019-10-12 [1] Github (tidyverse/glue@71eeddf)
##  htmltools       0.4.0      2019-10-04 [1] CRAN (R 3.5.2)                 
##  httr            1.4.1      2019-08-05 [1] CRAN (R 3.5.2)                 
##  jsonlite        1.6        2018-12-07 [1] CRAN (R 3.5.0)                 
##  knitcitations * 1.0.10     2019-09-15 [1] CRAN (R 3.5.2)                 
##  knitr           1.25       2019-09-18 [1] CRAN (R 3.5.2)                 
##  lattice         0.20-38    2018-11-04 [1] CRAN (R 3.5.3)                 
##  lubridate       1.7.4      2018-04-11 [1] CRAN (R 3.5.0)                 
##  magrittr        1.5        2014-11-22 [1] CRAN (R 3.5.0)                 
##  Matrix          1.2-17     2019-03-22 [1] CRAN (R 3.5.2)                 
##  memoise         1.1.0      2017-04-21 [1] CRAN (R 3.5.0)                 
##  pkgbuild        1.0.6      2019-10-09 [1] CRAN (R 3.5.2)                 
##  pkgload         1.0.2      2018-10-29 [1] CRAN (R 3.5.0)                 
##  plyr            1.8.4      2016-06-08 [1] CRAN (R 3.5.0)                 
##  prettyunits     1.0.2      2015-07-13 [1] CRAN (R 3.5.0)                 
##  processx        3.4.1      2019-07-18 [1] CRAN (R 3.5.2)                 
##  ps              1.3.0      2018-12-21 [1] CRAN (R 3.5.0)                 
##  R6              2.4.0      2019-02-14 [1] CRAN (R 3.5.2)                 
##  Rcpp            1.0.2      2019-07-25 [1] CRAN (R 3.5.2)                 
##  RefManageR      1.2.12     2019-04-03 [1] CRAN (R 3.5.2)                 
##  remotes         2.1.0      2019-06-24 [1] CRAN (R 3.5.2)                 
##  rlang           0.4.0      2019-06-25 [1] CRAN (R 3.5.2)                 
##  rmarkdown       1.16       2019-10-01 [1] CRAN (R 3.5.2)                 
##  rprojroot       1.3-2      2018-01-03 [1] CRAN (R 3.5.0)                 
##  sessioninfo     1.1.1      2018-11-05 [1] CRAN (R 3.5.0)                 
##  stringi         1.4.3      2019-03-12 [1] CRAN (R 3.5.2)                 
##  stringr         1.4.0      2019-02-10 [1] CRAN (R 3.5.2)                 
##  survival      * 2.44-1.1   2019-04-01 [1] CRAN (R 3.5.2)                 
##  testthat        2.2.1      2019-07-25 [1] CRAN (R 3.5.2)                 
##  usethis       * 1.5.1      2019-07-04 [1] CRAN (R 3.5.2)                 
##  withr           2.1.2      2018-03-15 [1] CRAN (R 3.5.0)                 
##  xfun            0.10       2019-10-01 [1] CRAN (R 3.5.2)                 
##  xml2            1.2.2      2019-08-09 [1] CRAN (R 3.5.2)                 
##  yaml            2.2.0      2018-07-25 [1] CRAN (R 3.5.0)                 
## 
## [1] /Library/Frameworks/R.framework/Versions/3.5/Resources/library

References

Avatar
Leyla Nunez
Statistician

Related

comments powered by Disqus