Xbar-R control chart for rational subgroups

Constructs a paired Xbar (subgroup mean) and R (subgroup range) chart for measurements organised in rational subgroups of size 2 to 10. Sigma is estimated from the average within-subgroup range.

Usage

shewhart_xbar_r(
  data,
  value,
  subgroup,
  rules = c("nelson_1_beyond_3s", "nelson_2_nine_same"),
  locale = getOption("shewhart.locale", "en"),
  verbose = NULL
)

Arguments

data

A data frame.

value

Tidy-eval column reference for the measurement.

subgroup

Tidy-eval column reference identifying the subgroup (e.g. shift, batch, hour). All subgroups must have equal size.

rules

Character vector of rule keys to apply. See shewhart_rules_available(). Default applies Nelson 1 and 2.

locale

One of "en", "pt", "es", "fr". Affects plot labels and informative messages.

verbose

Logical. Print progress messages? Defaults to the shewhart.verbose option.

Value

A shewhart_chart object of subclass shewhart_xbar_r.

Details

Xbar-chart limits use A2(n); R-chart limits use D3(n) and D4(n). See shewhart_constants() for the tabulated values.

References

Montgomery, D. C. (2019). Introduction to Statistical Quality Control (8th ed.). Wiley. Chapter 6.

Shewhart, W. A. (1931). Economic Control of Quality of Manufactured Product. D. Van Nostrand.

Examples

set.seed(1)
df <- data.frame(
  batch = rep(1:25, each = 5),
  y     = rnorm(125, mean = 50, sd = 1.5)
)
fit <- shewhart_xbar_r(df, value = y, subgroup = batch)
print(fit)
#> 
#> ── Shewhart chart Xbar-R ───────────────────────────────────────────────────────
#> • Observations / subgroups: 25
#> • Phase: "phase_1"
#> • Sigma estimate ("range"): 1.328
#> 
#> ── Control limits ──
#> 
#> # A tibble: 6 × 3
#>   chart line  value
#>   <chr> <chr> <dbl>
#> 1 Xbar  CL    50.2 
#> 2 Xbar  UCL   51.9 
#> 3 Xbar  LCL   48.4 
#> 4 R     CL     3.09
#> 5 R     UCL    6.53
#> 6 R     LCL    0   
#> ── Rule violations ──
#> 
#> ✔ No violations across 2 rules: "nelson_1_beyond_3s" and "nelson_2_nine_same".