Experiments with a second phase in the laboratory

It is common for the produce from field and other experiments to be processed in a laboratory. This results in a two-phase experiment, with the initial phase followed by a second, laboratory phase. Here, the laboratory assessment is to be interpreted broadly as a phase in which further processing, measurement, testing and so on are performed, even if, strictly speaking, a laboratory is not involved. Laboratory phases occur when there is to be the measurement of chemical attributes using equipment such as spectrometers, gas chromatographs or pH meters, testing using laboratory equipment, or the production of processed products such as wine, bread and malt that are subsequently assessed often by an expert panel. For some experiments both phases occur in the laboratory, such as in food processing when there is a phase in which mixtures are prepared, and a processing phase to produce the final product. Clinical trials can result in two phases, clinical and laboratory, when specimens from patients are processed in a laboratory. It would appear that such experiments occur frequently in the agriculture and other biological sciences. They all fit into the class of multiphase experiments, the simplest being two-phase experiments. Most of the examples published in the literature employ only one of the simplest types of multiple randomization.

Brien, C.J., Harch, B.D., Correll, R.L. and Bailey, R.A. (2011) present a general discussion of the design and analysis of two-phase experiments in which the second phase is a laboratory phase and in which orthogonal designs have been used. Brien (1983), Brien, May and Mayo (1987), Wood, Williams and Speed (1988, second example) and Brien and Payne (1999) give examples in which the second phase is a sensory evaluation of produce from the first phase. Smith et al. (2001) discussed the design and analysis of wheat experiments that involved a field and milling phase, and in which not all units from the field phase are processed in the milling phase. Cullis et al. (2003) described the design and analysis of a three-phase experiment that involved a field phase in which barley lines were grown, a malting phase in which barley malts were produced and a measurement phase in which several traits were determined. Again not all units from one phase continue on to subsequent phases. Smith et al. (2006) give general principles for the design of such experiments, while Smith et al., 2011 discuss the use of partial replication and sampling in later phases. Kerr (2003) noted that the microarray experiments can be the measurement phase of a two-phase experiment and Jarrett and Ruggiero (2008) recognize their two-phase nature. Brien and Bailey (2006, Examples 1, 4, 9, 12, 14 and 15, and Figure 7) are examples of experiments involving a first phase followed by a laboratory phase. A fuller list of examples is available