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Check the validity of a CHI number

Source: R/chi_check.R
chi_check.Rd

chi_check takes a CHI number or a vector of CHI numbers with character class. It returns feedback on the validity of the entered CHI number and, if found to be invalid, provides an explanation as to why.

Usage

chi_check(chi_number, check_mod11 = TRUE, check_mod10 = TRUE)

Arguments

chi_number

a CHI number or a vector of CHI numbers with character class.

check_mod11, check_mod10

Logical values (TRUE or FALSE, default is TRUE). By default, a CHI that passes either the modulo 10 or the modulo 11 check will be considered valid. Historically, CHIs only used modulo 11 for their check digit; however, starting in August 2026, some CHIs will only pass if they meet the modulo 10 criteria. Implementation of Mod 10 CHI numbers is scheduled for August 2026. From this date, CHI numbers are valid if they pass either a Mod 11 check or a Mod 10 check.

Value

chi_check returns a character string. Depending on the validity of the entered CHI number, it will return one of the following:

  • Valid CHI

  • Invalid character(s) present

  • Too many characters

  • Too few characters

  • Invalid date

  • Invalid checksum

  • Missing (NA)

  • Missing (Blank)

Details

The Community Health Index (CHI) is a register of all patients in NHS Scotland. A CHI number is a unique, ten-digit identifier assigned to each patient on the index.

The first six digits of a CHI number are a patient's date of birth in DD/MM/YY format.

The ninth digit of a CHI number identifies a patient's sex: odd for male, even for female. The tenth digit is a check digit, denoted checksum.

While a CHI number is made up exclusively of numeric digits, it cannot be stored with numeric class in R. This is because leading zeros in numeric values are silently dropped, a practice not exclusive to R. For this reason, chi_check accepts input values of character class only. A leading zero can be added to a nine-digit CHI number using chi_pad().

chi_check assesses whether an entered CHI number is valid by checking whether the answer to each of the following criteria is Yes:

  • Does it contain no non-numeric characters?

  • Is it ten digits in length?

  • Do the first six digits denote a valid date?

  • Is the checksum digit correct?

Examples

chi_check("0101011237")
#> By default, `chi_check()` now returns CHI numbers as valid if they pass either
#> a Mod11 or Mod10 check
#> Previously `chi_check()` would only return CHI numbers as valid if they pass a
#> Mod11 check - for this behaviour, please use `chi_check(chi_number, check_mod10
#> = FALSE)`
#> This message is displayed once per session.
#> [1] "Valid CHI"
chi_check(c("0101201234", "3201201234"))
#> [1] "Valid CHI"    "Invalid date"

library(dplyr)
df <- tibble(chi = c(
  "3213201234",
  "123456789",
  "12345678900",
  "010120123?",
  NA
))
df %>%
  mutate(validity = chi_check(chi))
#> # A tibble: 5 × 2
#>   chi         validity                    
#>   <chr>       <chr>                       
#> 1 3213201234  Invalid date                
#> 2 123456789   Too few characters          
#> 3 12345678900 Too many characters         
#> 4 010120123?  Invalid character(s) present
#> 5 NA          Missing (NA)