Statement regarding the retraction of the following research paper: “Improving usability and pregnancy rates of a fertility monitor by an additional mobile application: results of a retrospective efficacy study of Daysy and DaysyView app”

We are writing to inform our customers and users of our fertility tracker about criticisms of a study involving Daysy which have recently become public. The trial in question was conducted by researchers at the University Clinic of Erlangen (Germany) in order to investigate whether using the DaysyView app additionally increases the reliability of the Daysy fertility tracker.

It is the data collection methodology of the study which is the focus of the current controversy. The primary criticism of the methodology used is its retrospective design: i.e. after a period of time had elapsed, users were asked to look back and describe their use of Daysy. Further criticisms include the size of the sample studied and the selection criteria for the data evaluated. In the research paper published regarding the study, the authors reflected on the methodology used and submitted their data for publication to a journal, Reproductive Health.

Prior to publication, the results of the study were subject to peer review by other researchers; this is standard practice to ensure the good functioning of academic discourse. It was on the basis of the result of this evaluation that the journal decided to publish the data last year. Now, one year later, the editors in chief of the journal have decided to retract the publication. They state their reasons as doubts regarding the validity of the data expressed by an anonymous reviewer following publication. In view of the fact that these concerns are predicated on assumptions we are not able to properly examine, we do not accept this assessment and remain convinced of the quality of the results of the study. Moreover, this retraction has taken far longer than usual, and there was a lack of transparency regarding the process. Nevertheless, the journal has made its decision, and we think it is right to inform you of what has transpired. Under the following link you will find the officially published clarification:

To date, we have used the results of the study on our website and our social media channels to show just how much precision Daysy offers in determining fertile and infertile days in the reproductive cycle. Due to the retraction, we have decided to stop using the data from the study for this purpose. We have made this decision out of respect for the principles of academic research and take the feedback given to us by fellow researchers very seriously, even if we do not agree with every point of criticism. Regardless, academic discourse remains for us a yardstick by which we measure ourselves. You can find more information about the level of accuracy Daysy offers and the studies we have carried out here:

In the coming months, we will be carrying out another major study about the accuracy of Daysy and will, of course, keep you informed as this research progresses. We know how important our fertility trackers are to the over 500,000 women worldwide who have benefited from our products over the last few decades. The trust our customers place in us – as well as their health and wellbeing – is the most important thing for us as an organisation. Our goal is to offer, with our fertility tracking devices, a tool for you to monitor your menstrual cycle and determine your fertile and infertile days with the highest degree of accuracy. 

Please feel free to contact us at any time if you have any questions regarding the reliability of Daysy. 

Valley Electronics AG 
Maneggstrasse 45
8041 Zürich
+41 44 577 68 69