Test whether the reporting-delay distribution drifts over time

Usage

test_delay_drift(
  x,
  ...,
  stat = c("median", "spread", "mean", "iqr"),
  method = c("hamed-rao", "yue-pilon", "block-bootstrap"),
  by_strata = FALSE,
  strata = NULL,
  mature_only = TRUE,
  level = 0.95,
  alpha = 0.05
)

Arguments

x

A tbl_now object.

...

Passed to the underlying modifiedmk function (e.g. nsim for "block-bootstrap").

stat

Which delay summaries to test: any of "median", "mean", "iqr" (q75 - q25) and "spread" (q90 - q10). Defaults to median + spread, i.e. one location and one dispersion statistic.

method

Trend test: "hamed-rao" (default; Hamed-Rao variance correction, modifiedmk::mmkh()), "yue-pilon" (Yue-Pilon, modifiedmk::mmky()) or "block-bootstrap" (block-bootstrap MK, modifiedmk::bbsmk()).

by_strata

Logical (default FALSE). When TRUE, the test is run separately per stratum.

strata

Character vector of columns to group on when by_strata = TRUE. NULL (default) uses the object's strata.

mature_only

Logical (default TRUE). Drop event dates after the level incompleteness cutoff before testing.

level

Completeness level for the maturity cutoff (default 0.95).

alpha

Significance level for the drift verdict column (default 0.05).

Value

A tibble with one row per stat x stratum: strata, stat, n (series length), tau, sens_slope (change in the statistic per period), statistic, p_value, method and a logical drift (p_value < alpha).

Details

Runs an autocorrelation-robust monotonic-trend test on the per-period, count-weighted delay summaries, to answer "do delays drift over time?" in a way that respects the fact that a delay series is correlated with itself.

For each requested stat (and each stratum) it builds the per-event-date series of that statistic and tests it for a monotonic trend with the modifiedmk package, which corrects the Mann-Kendall variance for serial autocorrelation. A plain Mann-Kendall (or an OLS slope) would be anti-conservative here, because positive autocorrelation shrinks the effective sample size.

By default the test uses only mature event dates (those on or before the level incompleteness cutoff), because the recent, not-yet-fully-reported dates would otherwise inject a spurious downward trend.

See also

plot_delay_drift()

Examples

data(denguedat)
dengue <- tbl_now(denguedat,
  event_date = "onset_week", report_date = "report_week", verbose = FALSE
)
test_delay_drift(dengue)
#> Warning: ! `test_delay_drift()` is experimental: results are not guaranteed and the
#>   interface may change.
#> ℹ Interpret a significant result as a potential trend change, not a confirmed
#>   one.
#> This warning is displayed once every 8 hours.
#> # A tibble: 4 × 9
#>   strata stat       n      tau sens_slope statistic p_value method    drift
#>   <chr>  <chr>  <int>    <dbl>      <dbl>     <dbl>   <dbl> <chr>     <lgl>
#> 1 all    median  1090 -0.00918   0           -0.243 0.808   hamed-rao FALSE
#> 2 all    spread  1090 -0.178     0           -2.32  0.0203  hamed-rao TRUE 
#> 3 all    mean    1090 -0.0974   -0.000163    -2.05  0.0399  hamed-rao TRUE 
#> 4 all    iqr     1090 -0.0880    0           -3.22  0.00127 hamed-rao TRUE