Module capability 

Process capability analysis.

Computes standard capability indices for assessing how well a process meets specification limits.

Indices

• Cp — Potential capability (spread vs tolerance)
• Cpk — Actual capability (centering considered)
• Pp, Ppk — Long-term performance indices
• Cpm — Taguchi capability (target deviation)

Sigma Level

• sigma_to_ppm — Convert sigma level to PPM defect rate
• ppm_to_sigma — Convert PPM defect rate to sigma level

References

• Montgomery (2019), Introduction to Statistical Quality Control, 8th ed.

Structs

CapabilityIndices

Computed capability indices.

CapabilityIntervals

Confidence intervals for the capability indices – see CapabilityIndices::intervals.

ConfidenceInterval

A two-sided confidence interval.

NonNormalCapabilityResult

Result of a Box-Cox-based non-normal capability analysis.

PercentileCapabilityResult

Result of percentile-based process capability analysis.

ProcessCapability

Input specification for process capability analysis.

Enums

CapabilityModel

The distribution family a percentile capability is computed from.

IntervalError

Why CapabilityIndices::intervals refused its arguments.

NonNormalCapabilityError

Errors that can arise from non-normal process capability analysis.

PercentileCapabilityError

Why a percentile capability was refused.

Constants

DEFAULT_LAMBDA_RANGE

The default λ search range, [-5, 5].

MIN_PERCENTILE_DATA

Fewest values the method accepts.

Functions

boxcox_capability

Compute process capability indices for non-normal data via Box-Cox transformation.

percentile_capability

Computes percentile-based process capability indices.

ppm_to_sigma

Converts a parts-per-million (PPM) defect rate to a sigma quality level.

sigma_to_ppm

Converts a sigma quality level to parts-per-million (PPM) defect rate.