Experimental versus control designs

Two Experimental versus control subjects One-at-a-time designs Factorial designs Fractional factorial designs Nested designs Special designs... 

Random allocation of animals to treatment groups is a prerequisite of good experimental design. If not carried out, it is not possible to be sure whether treatment versus control differences are due to treatment or to confounding by other relevant factors. The ability to randomize easily is a major advantage animal experiments have over epidemiology. 

Fig. 1. Targeted clinical trial design for evaluating a new experimental therapy. A biomarker classifier is developed for identifying those patients most likely to respond to the new treatment (E). Only those patients are randomized to E versus the control treatment. The patients predicted less likely to respond (marker negative) are off-study. The targeted design is most useful in cases where the biomarker classifier has a strong biological rationale for identifying responsive patients and where it may not be ethically advisable to expose marker negative patients to the new treatment.

Data Treatment. The experimental design of sample collection did not permit statistical comparison of the collection efficiencies of filter combinations versus concentrated HNO3 impingement. The laboratory chamber was designed to simulate field conditions and not provide a "closed" system in which the concentrations of Plictran could be controlled. 

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