get.plan {crossdes}R Documentation

Menu-Driven Construction of Carryover Balanced Experimental Designs

Description

This menu based function constructs and randomizes simple experimental designs for repeated measurements with one or two block variables. It is assumed that each subject is assigned to each treatment at most once. A maximum number of subjects in the study is also requested. There are up to five possible construction methods available. These construction methods and the characteristics of the resulting designs are described in Wakeling and MacFie (1995).

Usage

get.plan(trt, k = trt, maxsub = 1000)

Arguments

trt An integer > 1, giving the number of treatments.
k An integer in {2,...,trt} giving the number of periods.
maxsub The maximum number of subjects available.

Details

The five types of designs are: designs based on all possible treatment orders ("All combinations"), Williams designs ("Williams"), designs based on mutually orthogonal latin squares ("MOLS"), a combination of balanced incomplete block designs (BIBDs) and Williams designs ("Patterson") and the balanced minimal designs of Afsarinejad ("no BBD needed"). Some designs are only available for special combinations of treatment number and number of periods. Other designs may require too many subjects. Therefore, the possible choices available for the submittet values of trt, k and maxsub are determined. If there is no design available, the parameters may be changed interactively. If more than one design type is available the user has to choose one. The minimum number of subjects required for the designs is given and may be a criterion for selecting a design. All types of designs are balanced for first-order carryover effects. All types except the balanced minimal RMDs ("no BBD needed") are also balanced block designs. The user may want to construct a design for a multiple of the minimum number of subjects required to get closer to the preferred number of subjects. Once the design is chosen, the labels for the treatments and subjects are randomized and the design is displayed. The treatments are numbered 1,...,trt. The entry (i,j) of the design corresponds to the treatment the i-th subject gets in the j-th period.

Value

A matrix representing the experimental design.

Warning

There is a possible problem with this implementation of the "Patterson" approach:

For the construction of designs that combine BIBDs with Williams designs, the function find.BIB is called to search for a BIBD. If the necessary conditions for the existence of a BIBD are fulfilled, the "Patterson" approach always returns a design. This design will however not always be a BIBD! When using the patterson approach, please check the reulting design for balance using isGYD and isCbalanced.

It should be noted that this is a computational problem only, not a problem of the theoretical approach of Patterson (1951).

Note

The "All combinations" approach requires the package gtools.

Author(s)

Oliver Sailer sailer@statistik.uni-dortmund.de

References

Afsarinejad, K. (1983): Balanced repeated measurements designs. Biometrika 70, 199-204.

Patterson, H.D. (1951): Change-over trials. Journal of the Royal Statistical Society B 13, 256-271.

Patterson, H.D. (1952): The construction of balanced designs for experiments involving sequences of treatments. Biometrika 39, 32-48.

Wakeling, I.N. and MacFie, H.J.H. (1995): Designing consumer trials balanced for first and higher orders of carry-over effect when only a subset of k samples from t may be tested. Food Quality and Preference 6, 299-308.

Williams, E. J. (1949): Experimental designs balanced for the estimation of residual effects of treatments. Australian Journal of Scientific Research, Ser. A 2, 149-168.

See Also

all.combin, balmin.RMD, des.MOLS, williams, williams.BIB

Examples

## Not run: 
get.plan(10,4,60)  
  # "Patterson" or "no BBD needed"
get.plan(7,7,7000) 
  # "All combinations", "Williams" or "MOLS", "Williams" requires 
  # only 14 subjects, "All combinations" requires 5040.   
get.plan(5,5,5)    
  # Increase maxsub
## End(Not run)

[Package Contents]