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Two-standard-deviation band decision rule

Source: R/sced-band.R
scedTwoSDBand.Rd

Draws the Nelson (1984) 2-SD band from the baseline (A) phase - the baseline mean plus and minus two baseline standard deviations - and flags the intervention (B) phase for a systematic shift: the rule fires when a run of consecutive or more successive B points falls on the same side beyond the band.

Usage

scedTwoSDBand(
  A_data,
  B_data = NULL,
  improvement = c("increase", "decrease"),
  k = 2,
  consecutive = 2L
)

Arguments

A_data, B_data

Numeric baseline and intervention observations.

improvement

"increase" (default) or "decrease"; sets which side of the band counts as improvement.

k

Band half-width in baseline SDs (default 2).

consecutive

Number of successive out-of-band points that trigger the flag (default 2, Nelson's rule).

Value

An AnalysisResult (type = "sced_2sd") whose estimate is the logical decision, with result$mean, result$sd, result$upper, result$lower, result$outside (per-B-point side: -1/0/+1) and result$first_run_at (index of the first triggering point, or NA).

References

Nelson LS (1984). The Shewhart control chart - tests for special causes. Journal of Quality Technology, 16(4), 237-239. Applied to SCED in Gast & Ledford (2014).

See also

scedCelerationLine(), scedABAB()

Examples

scedTwoSDBand(c(10, 12, 11, 9, 10), c(15, 16, 17, 16, 18))
#> <AnalysisResult> sced_2sd 
#>   estimate: TRUE 
#>   method: 2-SD band 
#>   fields: estimate, ci_lower, ci_upper, mean, sd, upper, lower, outside, first_run_at, k, consecutive, improvement 
#>   provenance: 1 entr(ies)