A jack knife is a pocket knife that is put to many tasks, because it's ready to hand. Often there could be a better tool for the job, such as a screwdriver, a scraper, or a can-opener, but these are not usually pocket items. In statistical terms, the expression implies making do with what's available. Another simile, of an extreme situation, is the bootstrap: extricating oneself from a predicament by the only means available (Curran-Everett, 2009). These everyday terms have been applied to statistical methods that allow us to work with limited data and draw robust conclusions. We have already discussed permutation tests, which are similar in that they use only the data collected, and make no assumptions about the population (Drummond & Vowler, 2012). We noted that permutation tests become laborious with larger samples, and the same is true of the bootstrap tests, where the data sample is repeatedly resampled. These tests are quite recent developments, and require computers, and sadly have not yet been provided in many of the more general statistics software packages.
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