A critique of the practice of comparing control data obtained at a single time point to experimental data obtained at multiple time points.

Abstract

The normal circadian rhythm in DNA synthetic activity (DNA-SA) in the tip of the mouse tongue is presented. When this rhythm, obtained from mice which were not treated (NT) or handled, was compared to the rhythms obtained from mice treated with saline (SAL) or 25 mg/kg isoproterenol (IPR), no alteration in the rhythm was observed after either treatment. The conclusion from this chronobiological, experimental design was that IPR had no effect on DNA-SA in the tip of the tongue. However, when three single time points (08.00, 11.00 or 14.00) are selected from the SAL-treated, control rhythm and compared to the multiple time point data from the IPR-treated mice, three very different, statistically supported conclusions were reached. The common practice of obtaining data at only one time point in control animals and comparing these data to data obtained from drug-treated animals at multiple time points is an example of poor experimental design which results in erroneous conclusions and unnecessary confusion in the literature on in vivo research.