## Property Control Charts

Control charts were originally developed in the 1920s as a quality assurance tool for the control of manufactured products. Although there are many types of control charts, the most common in a quality assessment program is a property control chart … Continue reading

## Prescriptive Approach to Quality Assurance

Illustrated here is an example of a prescriptive approach to quality assurance for laboratories monitoring waters and wastewaters, adapted from Environmental Monitoring and Support Laboratory, U. S. Environmental Protection Agency, “Handbook for Analytical Quality Control in Water and Wastewater Laboratories,” March … Continue reading

## Collaborative Testing and Two-Sample Plots

When an analyst performs a single analysis on a sample the difference between the experimentally determined value and the expected value is influenced by three sources of error: random errors, systematic errors inherent to the method, and systematic errors unique … Continue reading

## Modeling Response Surfaces Using Factorial Designs

In many cases the underlying theoretical relationship between the response and its factors is unknown. We can still develop a model of the response surface if we make some reasonable assumptions about the underlying relationship between the factors and the … Continue reading

## Simplex Optimization

One strategy for improving the efficiency of a searching algorithm is to change more than one factor at a time. A convenient way to accomplish this when there are two factors is to begin with three sets of initial factor … Continue reading

## One-Factor-at-a-Time Searching Algorithm

A simple algorithm for optimizing the response for a system is to adjust independently each factor. Consider a response that depends on two factors. We begin by optimizing the response for one factor by increasing or decreasing its value, holding … Continue reading

## Finding the Optimum Response Using a Searching Algorithm

If we know the equation for a response surface, then it is relatively easy to find the optimum response. Unfortunately, we rarely know any useful details about the response surface. Instead, we must determine the response surface’s shape and locate … Continue reading

## Response Surfaces

One of the most effective ways to think about an optimization is to visualize how a system’s response changes when we increase or decrease the levels of one or more of its factors. We call a plot of the system’s … Continue reading