Period-tracking apps may be inaccurate: study

Smartphone apps designed to track women's period cycles often disappoint users with a lack of accuracy, and may wrongly predict when it is safe to have intercourse, a new study has found. Researchers from University of Washington (UW)in the US collected data from about 2,000 reviews of popular period tracking apps, surveyed 687 people and conducted in-depth interviews with a dozen respondents. Nearly half of the survey respondents used a smartphone app to track their periods for a variety of reasons: to understand their body and reactions to different phases of their cycles; to prepare for their periods; to achieve or avoid pregnancy; or to inform conversations with healthcare providers.

Researchers focused on nine different period tracking apps, and on what characteristics users liked or disliked. They found that while some apps were more successful in meeting users' needs, none were perfect. Women participants found the modelling assumptions used in some period tracking apps were not accurate or flexible enough to consistently predict their menstrual cycles, particularly when their periods were not regular. Many apps do not allow users to correct them when the predictions are wrong or to input data or explanations about why a particularly stressful month or change in birth control might have thrown off their cycles, researchers said. "In some cases, you do not have a way to go in and say I missed my period because of x reason or because I was in the hospital - both ordinary and exceptional circumstances can mess up the algorithms because they are not really robust," said Nikki Lee from UW.

"The apps are most accurate if your cycles are really regular, but the people who most need an app are the people whose cycles are not regular," Lee said. Apps rarely allow women to customise results or how they are presented. Someone who is trying to avoid getting pregnant or to prepare for their period, for instance, might want an app to provide a more generous window for predicting when they are ovulating or when their period will arrive so they are not surprised, researchers said.

Someone trying to become pregnant would likely want the app to zero in on a narrower span of time when their chances of ovulation are highest, they said.

"People did not feel like the apps were very good at supporting their particular needs or preferences. People felt they were better than tracking their periods on paper, but still were not great in a lot of basic ways," said Daniel Epstein, from UW.

"One significant issue is that few apps are transparent about explaining their methodology or limitations," said Julie Kientz, associate professor at UW. In working with healthcare providers on a teen health app, she learned that teenage girls were relying on smartphone apps as their primary form of birth control to tell them when they should avoid having sex. "That's pretty disconcerting because accuracy can be a problem with these apps," Kientz said.