An example of an analogy drawing upon a chemical concept to explain another idea (from research methods, 'testing for initial equivalence'):
"…many studies rely on testing for a statistically significant difference, although this is a very dubious criterion for equivalence….
The results are analysed to see if there is a very unlikely difference between the scores in the different conditions. If a statistically significant difference is found, then this clearly suggests the groups cannot be considered equivalent. That is reasonable.
Unfortunately the reverse does not apply: if the differences do not reach significance, we cannot assume that implies equivalence. Say p=0.08 (which means that the differences were unlikely enough to only occur by chance about once in 12 times, rather than once in twenty times as when p=0.05), this still shows there was a difference that was unlikely to be down to random factors. There is a logical difference between what we are seeking to do in these two situations. In one case (comparing post-test results), we are trying to exclude all but those outcomes that are most unlikely to be chance events, and in the other (comparing pre-test scores), we are trying to show that any difference is small enough to be insignificant in affecting later outcomes. So, in the first case, we are trying to show something is very improbable, but in the other case, we are trying to show we have a very probable outcome. So, using the same kind of inferential test as a test of equivalence means (sensibly) excluding cases with very different pre-test outcomes across treatments from being labelled equivalent: but still (dubiously) admitting other substantially different pre-test outcomes across treatments as being equivalent.
Read examples of scientific analogies
Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.