Design of Experiments Guide
Introduction to DOE
Overview of Design of Experiment Platforms
The JMP DOE platforms help you to design, evaluate, and analyze experiments. Most of the platforms focus on constructing designs. Other platforms support the design effort. This section provides a quick overview of each of the platforms found under the DOE menu.
Design Construction Platforms
Custom Design
Constructs designs that fit a wide variety of settings. Custom designs tend to be more cost effective and flexible than approaches based exclusively on classical designs.
Custom designs accommodate various types of factors, constraints, and disallowed combinations. You can specify which effects are necessary to estimate and which are desirable to estimate, given the number of runs. You can specify a number of runs that matches the budget for your experimental situation. Custom designs also support hard-to-change and very-hard-to-change factors, allowing you to construct split-plot and related designs.
The Custom Design platform constructs many special design types:
– screening
– response surface
– mixture
– random block
– split-plot
– split-split-plot
– two-way split-plot
You can construct classical screening, response surface, and mixture designs using other platforms. However, the Custom Design platform gives you flexibility that is not available in the other platforms. Constructing designs for split-plot situations can be done only using the Custom Design platform.
Definitive Screening Design
Constructs screening designs for continuous and two-level categorical factors. Definitive screening designs are useful if you suspect active interactions or curvature. Definitive screening designs enable you to identify the source of strong nonlinear effects while avoiding complete confounding between any effects up through the second order.
Definitive screening designs are most appropriate for experimentation with four or more factors. Definitive screening designs support grouping runs into blocks. The number of blocks is user-specified.
Screening Design
Constructs screening designs for continuous, discrete numeric, and categorical factors with an arbitrary number of levels. When standard designs exist, you have two options:
– Choose from a list of classical screening designs. These designs allow two-level continuous factors or two- or three-level categorical or discrete continuous factors.
– Generate a design that is orthogonal or nearly orthogonal for main effects. Near-orthogonal designs allow for categorical and discrete numeric factors with any number of levels, as well as two-level continuous factors. These designs focus on estimating main effects in the presence of negligible interactions.
For many screening situations, standard designs are not available. In these situations, you can construct near-orthogonal screening designs.
Response Surface Design
Constructs designs that model a quadratic function of continuous factors. To fit the quadratic effects, response surface designs require three settings for each factor. JMP provides response surface designs for up to eight factors.
You can choose from a list of Central Composite or Box-Behnken designs. When appropriate, Central Composite designs that block orthogonally are included in the list. Various modifications to Central Composite designs are supported.
Full Factorial Design
Constructs full factorial designs for any number of continuous or categorical factors, both with arbitrarily many levels. A full factorial design has a run at every combination of settings of the factors. Full factorial designs tend to be large. The number of runs equals the product of the numbers of factor levels.
Mixture Design
Constructs designs that you use when factors are ingredients in a mixture. In a mixture experiment, a change in the proportion of one ingredient requires that one or more of the remaining ingredients change to maintain the sum. Choose from among several design types, including some classical mixture design approaches: optimal, simplex centroid, simplex lattice, extreme vertices, ABCD, and space filling. For optimal, extreme vertices, and space filling mixture designs, you can specify linear inequality constraints to limit the design space.
Taguchi Arrays
Constructs designs that you use for signal-to-noise analysis. The designs are based on Taguchi’s inner and outer array approach. Control factor settings constitute the inner array and noise factor settings form the outer array. The mean and signal-to-noise ratio are the responses of interest.
An alternative to using a Taguchi array is to construct a custom design that includes control factors, noise factors, and control-by-noise interactions. Such designs, called combined arrays, are generally more cost-effective and informative than Taguchi arrays.
Choice Design
Constructs designs that you can use to compare prospective products. The factors in a choice design are product attributes. The design arranges product profiles, which are combinations of various attributes, in pairs or in groups of three or four. The experiment consists of having respondents indicate which profile in a pair of profiles that they prefer. You can generate a choice design that reflects prior information about the product attributes.
MaxDiff
Constructs a design consisting of choice sets that can be presented to respondents as part of a MaxDiff study. Respondents report only the most and least preferred options from among a small set of choices. This forces respondents to rank options in terms of preference, which often results in rankings that are more definitive than rankings obtained using standard preference scales.
Covering Array
Constructs combinatorial designs that you can use to test software, networks, and other systems. A strength t covering array has the property that every combination of levels of every t factors appears in at least one run. Covering arrays allow for any number of categorical factors, each with an arbitrary number of levels. Disallowed combinations can be specified.
Space Filling Design
Constructs designs for situations where the system of interest is deterministic or near-deterministic. A standard application involves creating a simpler surrogate model of a highly complex deterministic computer simulation model.
In a deterministic system, there is no variation. The goal is to minimize the difference between the fitted model and the true model (bias). Space-filling designs attempt to meet this goal either by spreading the design points out as far from each other as possible or by spacing the points evenly over the design region.
JMP provides seven space-filling design approaches. One of these approaches, the fast flexible filling design, accommodates categorical factors with any number of levels and supports linear constraints.
Accelerated Life Test Design
Constructs and augments designs useful for testing products at extreme conditions which are intended to accelerate failure time. Use experimental results to predict reliability under normal operating conditions.
The life distribution can be lognormal or Weibull. Designs can include one or two accelerating factors. If there are two accelerating factors, you can choose to include their interaction. You can specify prior distributions for the acceleration model parameters. D-optimal and two types of I-optimal designs are available.
Nonlinear Design
Constructs and augments designs that you use to fit models that are nonlinear in their parameters. You can construct a design using estimates from a model fit to existing data. You can also construct a design by applying prior knowledge if you do not have model-based estimates.
Balanced Incomplete Block Design
Constructs design for testing a treatments in b blocks where only k treatments (k < a) can be run in any one block
Group Orthogonal Supersaturated Design
Constructs supersaturated screening designs. They are appropriate in early stage work when the number of factors to be investigated is larger than the number of feasible runs. A group orthogonal supersaturated design is a special class of two-level supersaturated designs with properties that are desirable for model selection.
Supporting Platforms
Augment Design
Adds runs to existing designs in such a way that the resulting design is optimal. Augment Design enables you to conduct experiments in an iterative fashion. You can replicate the design, add center points, create a fold-over design, add axial points, add points to create a space-filling design, or augment the design with a specified number of runs. You can group runs into blocks to distinguish the original runs from the augmented runs. You can add model effects that were not in the original model and specify requirements for these effects.
Fit Definitive Screening Design
Analyzes definitive screening designs using a methodology called Effective Model Selection for DSDs. This methodology takes advantage of the special structure of definitive screening designs.
Fit Group Orthogonal Supersaturated
Analyzes group orthogonal supersaturated designs. This analysis technique takes advantage of the group orthogonal structure of group orthogonal supersaturated designs.
Evaluate Design
Provides diagnostics for an existing experimental design. The Evaluate Design platform provides various ways for you to assess the strengths and limitations of your design. The platform can be used with any data table, not only designs created using JMP.
Several diagnostics are provided:
– power analysis
– prediction variance plots
– estimation efficiency for parameters
– the alias matrix, showing the bias structure for model effects
– a color map showing absolute correlations among effects
– design efficiency values
Compare Designs
Compares up to four designs to a reference design. Use to explore, evaluate, and compare design performance. Diagnostics show how the designs perform relative to each other and how they perform in an absolute sense.
Sample Size and Power
Provides sample size and power calculations for a variety of testing situations: one or more sample means, a standard deviation, one or two proportions, counts per unit (Poisson mean), and sigma quality level. For these options, you specify two of three quantities to compute the third. These three quantities are the difference you want to detect, the sample size, and the power. If you supply only one of these values, a plot of the relationship between the other two values is provided.
You can compute the sample size required for a reliability test plan, where your goal is to estimate failure probabilities. You can also compute the sample size required for a reliability demonstration, where your goal is to demonstrate that a product meets or exceeds a specified standard.