Example code in vignette gives short_group warning that appears incorrect

[francisbarton]

As seen in deviations.Rmd.

Each group has 12 points as can be seen in the output from summary() below.

However the warning message still appears, suggesting that "some groups have... < 12 observations".

reprex:

NHSRdatasets::ae_attendances |>
  dplyr::summarise(across("attendances", sum), .by = "period") |>
  NHSRplotthedots::ptd_spc(
    value_field = "attendances",
    date_field = "period",
    rebase = as.Date(c("2017-04-01", "2018-04-01"))
  ) |>
  summary()
#> Warning in ptd_add_short_group_warnings(.): Some groups have 'n < 12'
#> observations. These have trial limits, which will be revised with each
#> additional observation until 'n = fix_after_n_points' has been reached.
#> Plot the Dots SPC options:
#> ===================================
#> value_field:          'attendances'
#> date_field:           'period'
#> facet_field:          not set
#> rebase:               '2017-04-01'
#> rebase:               '2018-04-01'
#> fix_after_n_points:   not set
#> improvement_direction:'increase'
#> target:               not set
#> trajectory:           not set
#> screen_outliers:      'TRUE'
#> -----------------------------------
#> # A tibble: 3 × 9
#>   rebase_group mean_col     lpl    upl     n common_cause special_cause_improv…¹
#>          <dbl>    <dbl>   <dbl>  <dbl> <int>        <int>                  <int>
#> 1            0 1946858.  1.64e6 2.25e6    12           12                      0
#> 2            1 1985843.  1.73e6 2.24e6    12           12                      0
#> 3            2 2068915.  1.81e6 2.33e6    12           12                      0
#> # ℹ abbreviated name: ¹​special_cause_improvement
#> # ℹ 2 more variables: special_cause_concern <int>, variation_type <chr>

^{Created on 2024-08-08 with reprex v2.1.1}

Should the warning say <= 12 or is it being incorrectly triggered?

[francisbarton]

The code that generates the warning is in ptd_add_short_group_warnings.R:

warning_threshold = getOption("ptd_spc.warning_threshold", 13))

As 12 < 13, the warning is being triggered by groups where n = 12. Either the fallback value here needs to be set to 12, or the warning needs to say that:

Some groups have 'n <= 12' observations

or (more accurately, given the code above):

Some groups have 'n < 13' observations