Critics of personal science and self-experimentation might try to argue that because personal science deals with a sample size of one, that there is no ability to generalize the results of experiments. But, there is a fallacy in that logic. While it is clear that experimenting on a single subject cannot prove that the same results will absolutely occur for others, by inferential statistics it does clearly show that there is a high probability that it could work for at least some other people. Further, it should be noted that most health science and social science research also never shows that something will absolutely work for everyone, but instead shows a statistical probability that a result will occur. Using this concept of generalizing the result of personal science by determining the possibility that it may work for others should become part of most personal science research methodologies.
There is another vital area where personal science and self-experimentation can lead to generalization, and that is by having personal science being a component of traditional science. Because, while an experiment on only a single subject may be able to show the possibility of the same results occurring with someone else, if a sufficient number of people follow similar methodologies in their self-experimentation, then the group of their results can be used with traditional scientific methods to determine a statistical likelihood of how the results might occur across a broader range of people. This in effect becomes the crowd sourcing of science, which some are now calling “citizen science”.
This use of personal science may be especially valuable in the repetition of experimentation after initial professional scientific studies. This is because there is a sociological bias towards having scientists wishing to do “groundbreaking” work of discovering new knowledge, but not as much desire to do the ongoing work of continuing to test initial results. But, if the results of a professional scientific study shows something that may be beneficial to individuals, then there is a motivation for individuals who are aware of the results of the study to attempt to implement the results in their personal lives, and if a sufficient number of people do this in a sufficiently rigorous manner, this data can be used along with the initial research and follow-up research in a meta-analysis to create an improved statistical model.
Thus personal science has at least two major areas that it can help add to the general body of scientific knowledge, which in some ways are the “bookends” to professional science. On one side, initial self-experimentation can show the possibility of results potentially occurring for others, which can spur a fuller study with more subjects to occur. And on the other side, from the results of professional science, the crowd sourcing of personal science can help to improve the accuracy of knowledge derived through the professional studies.