Good study design

As stated above, one fundamental of good study design is the creation of patient selection criteria that will result in a study population that is truly representative of the entire target population without inadvertent bias in the patient enrollment. This and other fundamentals of good study design are discussed below. 

The study design is an important element in assessment of quality protocols. The overall purpose of the study design is to reduce the variability or bias inherent in all research. Good study design will always address control methods that reduce experimental bias. These control methods will often include treatment blinding, randomization and between- or within-patient study designs. The Schedule of Assessments describes a schedule of time and events and provides a complete... 

At this stage in planning, the essential study design information listed below should be determined and a written study plan (i.e., protocol) including these key study details prepared. A formal, pre-approved study plan is required for field soil dissipation studies conducted under Good Laboratory Practice (GLP). A written study plan for non-GLP studies is highly recommended since the document serves as valuable guidance for study personnel. 

Much of what is done (and how it is done) in repeat-dose studies is a response to a number of regulations. Three of these have very broad impact. These are the Good Laboratory Practices requirements, Animal Welfare Act requirements, and regulatory requirements that actually govern study design. 

The likely effectiveness of the product, derived from the preclinical and early clinical work, will determine study design, complexity and size. It is a mistake to try to answer too many questions in a single study, despite the apparent commercial attractiveness of such a strategy. A study overburdened by many secondary objectives is more likely to fail when the design is implemented in many centres worldwide. What seems a good idea in head office can often be hard to implement in the clinic. Statistical advice is vital, and statisticians offer excellent opinions about the utility of complex study designs. 

However, most public concern does not center around death or other acute intoxication symptoms, but rather those chronic injuries which we term as irreversible. These are carcinogenesis (cancer), teratogenesis (birth defects), or mutagenesis (genetic defects). There have been three good studies involving the ability of 2,4-D to cause cancer. The conclusion by the authors of these three studies is that there is no evidence that 2,4-D causes cancer. However, the study design was such that they were not adequate to prove that 2,4-D could not cause cancer, and as a result, further cancer studies were required by the EPA which should provide a definitive answer. 

The most critical and difficult prerequisite for a good study is to select an important feasible question to answer. Accomplishing this is a consequence primarily of biological knowledge. Conceptual simplicity in design and analysis is a very important feature of good trials. Good trials are usually simple to analyze correctly. 

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