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These can be represented by their SDs, SD animal and SD cell, respectively. There are two sources of variation in such an experiment: (i) variation among animals and (ii) variation among cells isolated from an individual animal. While I am sure that most readers need no convincing that it is invalid to study a single animal, the literature contains many studies where, say, three animals are used and five cells are studied from each animal. For example, is Ca 2+ handling or ion channel kinetics or density different in the two conditions?

In many such projects, the question is whether the properties of cells or tissues are different between the two groups of animals or people. In tissue culture experiments, comparisons can be made between cells transfected with active and scrambled siRNAs. Tissue may also be taken from human subjects: for example, diabetic versus healthy or pregnant versus control.

For example, a comparison may be between wild type and transgenic, control and heart failure, or naive and conditioned. A common example arises in physiology experiments comparing tissues or cells that come from two or more groups in order to investigate whether the groups differ. The purpose of this tutorial is to concentrate on one statistical issue that, although widely discussed ( Lazic, 2010 Sikkel et al., 2017 Lazic et al., 2018), is still a major problem: this is the subject of pseudoreplication ( Hurlbert, 1984) in which data points are treated as independent biological estimates when they are really technical replicates.

Brown university graphpad prism serial number