[Solved] Electric heating pads can be safely left in place up to 1 hour if the patient does not report any problems with circulation. Hypothesized Mean Difference: The presumed difference between the means of two populations or conditions being compared in a statistical hypothesis test. Two-Tail: A term used in statistics referring to the two-tailed test of significance that checks for the possibility of positive or negative differences. Observations: The act of noting and recording something with instruments or the naked eye as part of a scientific or empirical study. Untreated Population: A group in a study or an experiment that does not receive the treatment or intervention being tested.