Compare revision delays between confirmed and retracted cases

A negative result often comes back faster than a positive one – or slower, if positives are prioritised. Either way the delay from report to resolution is not the same distribution for the two outcomes, and a nowcast that assumes it is will be wrong about how many pending cases are still to be confirmed.

diagnose_revision_delay() compares the two delay distributions; plot_delay_distribution() with axis = "revision" shows them.

Usage

diagnose_revision_delay(x, by = NULL)

Arguments

x

A tbl_now with a revision process.

by

Optional stratum column to compare within; NULL (default) pools.

Value

diagnose_revision_delay() returns a one-row-per-comparison tibble with stratum, n_confirmed, n_retracted, median_confirmed, median_retracted, difference, statistic and p.value.

The test

A two-sided Wilcoxon rank-sum test on the revision delays. It is used rather than a t-test because reporting delays are strongly right-skewed and frequently have a point mass at zero, so a difference in means is neither robust nor the quantity of interest – what matters is whether one outcome resolves systematically sooner.

A small p-value says the two delay distributions differ. It does not say the difference matters: with tens of thousands of records a one-hour difference is significant and irrelevant, so read difference (the gap in median days) alongside it.

Rows with a missing or negative delay are dropped, and how many is reported in the dropped attribute of the result. A negative revision delay means the record is revised before it was reported, which the timeline forbids.

See also

add_revision_date() to attach a revision process; censor_revision_delays_above() for resolutions that never arrive; revised_cases for counting the outcomes; plot_delay_distribution() with axis = "revision" for the picture of the same comparison; diagnose_drift() for the same question about the reporting delay over time. The Diagnosing a tbl_now article puts this alongside the other checks.

Examples

cases <- data.frame(
  onset = as.Date("2021-01-04") + rep(0:9, each = 4),
  visit = as.Date("2021-01-05") + rep(0:9, each = 4),
  result = as.Date("2021-01-05") + rep(0:9, each = 4) +
    rep(c(1, 1, 5, 6), times = 10),
  outcome = rep(c("confirmed", "confirmed", "retracted", "retracted"), times = 10)
)
flu <- tbl_now(cases,
  event_date = onset, report_date = visit,
  revision_date = result, revision_type = outcome,
  data_type = "linelist", verbose = FALSE
)

# Retractions here come back about four days later than revisions, and
# the test says so.
diagnose_revision_delay(flu)
#> # A tibble: 1 × 8
#>   stratum n_confirmed n_retracted median_confirmed median_retracted difference
#>   <chr>         <int>       <int>            <dbl>            <dbl>      <dbl>
#> 1 all              20          20                1              5.5       -4.5
#> # ℹ 2 more variables: statistic <dbl>, p.value <dbl>

# The same comparison as a picture.
plot_delay_distribution(flu, axis = "revision")