Blog of the Society for Menstrual Cycle Research

Getting from the Average to the Individual When Reading Reports of Research

December 10th, 2012 by Paula Derry

We are unique individuals. Or, we are like everyone else. Which is it? For menstrual periods and the menopausal transition, as perhaps for most things, we’re a little bit of both. For me, keeping in mind that both are somehow true, and understanding the ways in which each is true, is a crucial but tricky business. Scientific findings are often reported as though they are universal truths. “The normal menstrual cycle is regular and occurs every 28 days.” “Depression is more likely during the transition to menopause.” However, research most typically examines groups of people, and results are most often average findings. A discrepancy between the average and the range of real experience isn’t surprising.

Take, for example, a study of the transition to menopause. This was longitudinal research—that is, the same group of women was studied for many years, and the patterns of change in their menstrual cycles over time could be documented. The authors conclude that there are three stages in the transition to menopause. At first women experience, perhaps beginning in their thirties, subtle changes in menstrual flow (like periods becoming heavier or lighter) without cycle length becoming irregular. Next, periods become irregular. Finally, women skip periods in the run-up to menopause. The stages are based on what, in the authors’ words, occurs “most frequently”; the average or frequent result is the basis for understanding the underlying pattern. Yet there is also a lot of variation. As reported in the article, only 39% of the women progressed in a forward manner through the three stages. Almost half seesawed back and forth. In addition, it is known that a significant minority of women report that they have gone from regular cycle lengths straight to menopause without a time of menstrual irregularity. I remember that when I first read this study I felt a certain comfort that changes in my body, like lighter periods and other changes, were predictable and fit into a pattern that other women experience. Yet, on the other hand, the findings can’t be used as a blueprint for what is supposed to happen. We share experiences with others, but we’re also unique individuals.

The average menstrual cycle is said to be 28 days—well, I don’t know many women with a 28-day cycle, and while some women describe themselves as “regular as clockwork” other women are bewildered that anyone could think that the cycle was regular. Rates of depression have been found in many studies to increase during the menopausal transition. However, the great majority of women do not become depressed (the “relative risk” has increased, but the “absolute risk” remains low). Knowing that the rate increases might suggest to a woman that she consider this possibility, but does not answer the question of whether she will become depressed, or, if she does, whether her depression is related to perimenopause or something else.

In trying to use scientific facts to understand ourselves or the world around us, the difference between the particular and the general, the predictable and the unpredictable, is important. Our individual behavior and physiology aren’t random or without form, but neither are they completely predictable.

  

2 Responses to “Getting from the Average to the Individual When Reading Reports of Research”

  1. Thanks, Paula.
    As a woman and as a clinician-scientist I believe it is useful to know the average but also to know how much individual variation there is around that average.
    That’s why, when I show data from women in studies I have done, I like to show each person’s result as a dot (scatter plot). So, often, it looks like a cloud of dots. Then we draw in the average.
    That allows women, other physicians and scientists, to see both the forest and the tree.

  2. Paula Derry says:

    I like that idea, of showing a scatter plot of each person’s results. It makes a lot of sense.

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