An economic-statistical design of the joint and S control charts with double sampling and variable sampling intervals

Abstract

A combination of double sampling and variable sampling interval (DSVSI) charts can increase the efficiency of signaling small shifts . This study proposes an economic-statistical model for designing joint DSVSI and s charts. The proposed approach uses the economic model developed by Duncan in 1956. Research results indicate that the economic-statistical design of the joint DSVSI and s charts outperformed traditional economic design approach in detection abilities of process shifts; variable cost (a₂), expected costs resulting from defective products when the process was in control (C₀), and the expected number of assignable causes (λ) have the major influence on cost E(C′); deviations (δ, γ) significantly influenced cost E(C′); and statistical limitations () do not substantially affect cost E(C′).

Keywords:

• double sampling
• economic-statistical
• variable sampling intervals
• and s control charts