np chart for the number of nonconforming items

Constructs an np chart from counts of nonconforming items in subgroups of constant size n. For variable subgroup sizes, use shewhart_p() instead.

Usage

shewhart_np(
  data,
  defects,
  n,
  index = NULL,
  rules = c("nelson_1_beyond_3s"),
  locale = getOption("shewhart.locale", "en"),
  verbose = NULL
)

Arguments

data: A data frame.
defects: Tidy-eval column reference for the count of nonconforming items in each subgroup.
n: Numeric scalar. The (constant) subgroup size.
index: Optional tidy-eval column reference for the x-axis.
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_np.

References

Montgomery, D. C. (2019). Introduction to Statistical Quality Control (8th ed.). Wiley. Chapter 7.2.2.

Examples

set.seed(1)
df <- data.frame(
  day     = 1:30,
  defects = rbinom(30, size = 200, prob = 0.04)
)
fit <- shewhart_np(df, defects = defects, n = 200, index = day)
print(fit)
#> 
#> ── Shewhart chart np (number of nonconforming) ─────────────────────────────────
#> • Observations / subgroups: 30
#> • Phase: "phase_1"
#> • Sigma estimate ("binomial"): 2.799
#> 
#> ── Control limits ──
#> 
#> # A tibble: 3 × 3
#>   chart line  value
#>   <chr> <chr> <dbl>
#> 1 np    CL     8.17
#> 2 np    UCL   16.6 
#> 3 np    LCL    0   
#> ── Rule violations ──
#> 
#> ✔ No violations across 1 rule: "nelson_1_beyond_3s".