Use of Measurements Controls and Statistics

Suppose you wanted to test the hypothesis that a regular exercise program causes people to have a lower resting heart rate.

The Study of Body Function

First, you would have to decide on the nature of the exercise program. Then, you would have to decide how the heart rate (or pulse rate) would be measured. This is a typical problem in physiology research, because the testing of most physiological hypotheses requires quantitative measurements.

The group that is subject to the testing condition—in this case, exercise—is called the experimental group. A measurement of the heart rate for this group would only be meaningful if it is compared to that of another group, known as the control group. How shall this control group be chosen? Perhaps the subjects could serve as their own controls—that is, a person's resting heart rate could be measured before and after the exercise regimen. If this isn't possible, a control group could be other people who do not follow the exercise program. The choice of control groups is often a controversial aspect of physiology studies. In this example, did the people in the control group really refrain from any exercise? Were they comparable to the people in the experimental group with regard to age, sex, ethnicity, body weight, health status, and so on? You can see how difficult it could be in practice to get a control group that could satisfy any potential criticism.

Another potential criticism could be bias in the way that the scientists perform the measurements. This bias could be completely unintentional; scientists are human, after all, and they may have invested months or years in this project! Thus, the person doing the measurements often does not know if a subject is part of the experimental or the control group. This is known as a blind measurement.

Now suppose the data are in, and it looks like the experimental group indeed has a lower average resting heart rate than the control group. But there is overlap—some people in the control group have measurements that are lower than some people in the experimental group. Now, is the difference in the average measurements of the groups due to a real, physiological difference, or is it due to chance variations in the measurements? Scientists attempt to test the null hypothesis (the hypothesis that the difference is due to chance) by employing the mathematical tools of statistics. If the statistical results so warrant, the null hypothesis can be rejected and the experimental hypothesis can be deemed to be supported by this study.

The statistical test chosen will depend upon the design of the experiment, and it can also be a source of contention among scientists in evaluating the validity of the results. Because of the nature of the scientific method, "proof" in science is always provisional. Some other researchers, employing the scientific method in a different way (with different measuring techniques, experimental procedures, choice of control groups, statistical tests, and so on) may later obtain different results. The scientific method is thus an ongoing enterprise.

The results of the scientific enterprise are written up as research articles, and these must be reviewed by other scientists who work in the same field before they can be published in peer-reviewed journals. More often than not, the reviewers will suggest that certain changes be made in the articles before they can be accepted for publication.

Examples of such peer-reviewed journals in which articles pertaining to many scientific fields are published include Science (www.sciencemag.org/), Nature (www.nature.com/nature/), and Proceedings of the National Academy of Sciences (www.pnas.org/).

Review articles in physiology can be found in Annual Review of Physiology (physiol.annualreviews.org/), Physiological Reviews (physrev.physiology.org/), and News in Physiological Sciences (www.the-aps.org/publication/journals/ pub_nips_home.htm). Medical research journals, such as the New England Journal of Medicine (content.nejm.org/) and Nature Medicine (www. nature.com/nm/), also publish articles of physiological interest. There are also a great number of specialty journals in areas of physiology such as neurophysiology, endocrinology, cardiovascular physiology, and so on.

Students who wish to look online for scientific articles published in peer-reviewed journals that relate to a particular subject can do so at the National Library of Medicine website, PubMed (www.ncbi.nlm.nih.gov/entrez/query.fcgi).

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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