Introduction: Inappropriate design of experimental studies in medicine inevitably leads to inaccurate or false results, which serve as basis for erroneous and biased conclusions. Aim. The aim of our study was to investigate prevalence of implementing basic principles of experimental design (local control, replication and randomization) in preclinical experimental studies, performed either on animals in vivo, or animal/human material in vitro. Material and Methods. Preclinical experimental studies were retrieved from the PubMed database, and the sample for analysis was randomly chosen from the retrieved publications. Implementation rate of basic experimental research principles (local control, randomization and replication) was established by careful reading of the sampled publications and their checking against predefined criteria. Results. Our study showed that only a minority of experimental preclinical studies had basic principles of design completely implemented (7%), while implementation rate of single aspects of appropriate experimental design varied from as low as 9% to maximum 86%. Average impact factor of the surveyed studies was high, and publication date relatively recent, suggesting generalizability of our results to highly ranked contemporary journals. Conclusion. Prevalence of experimental preclinical studies that did not implement completely basic principles of research design is high, raising suspicion to validity of their results. If incorrect and biased, results of published studies may mislead authors of future studies and cause conduction of fruitless research that will waste precious resources.
Key words: randomization, control experiments, replication, internal validity.
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