Irregularity report

There is a new Irregularity report that is a successor to the old (and long retired) Regularity report. You will have seen on the Activities tab that a Diagnostic reading is available for most activities for which you recorded your heart rate. This can be especially useful as an early indication that your heart rate strap needs a new battery or is mis-performing or that there is an issue with your sports watch. If you a number of Check_Strap readings, this is likely to be the case.

For most activities that have a Diagnostic reading the value is Regular. You are also likely to occasionally see an activity flagged as either Irregular or Unclear. This relies on a Crickles algorithm that detects a particular kind of behaviour in the heart rate pattern. This is certainly not in any way a medical diagnostic nor does it aim to evaluate a range of potential cardiac irregularities. Nonetheless, analysis from Crickles survey responses show that respondents who report heart rhythm issues are more likely to have more “Irregular” readings in this specific sense than respondents who don’t, and the difference is statistically significant (p-value < 0.05). A large majority of Crickles users will see some Irregular readings but those with heart rhythm issues tend to see more.

The Irregularity report shows you how your “irregularity ratio” – the frequency with which Irregular readings crop up – compares to that for the all people who have responded to the Crickles survey. The report has the following elements:

1. Box plots in black showing the distribution of irregularity ratios for all survey respondents. Crucially, these are split between those who report a heart rhythm issue (top boxplot) and those who don’t (lower boxplot). If you’re not familiar with box plots there’s a handy guide here. (Note that the boxplot on the report is horizontal whereas the link describes box plots shown vertically – this is purely presentational.)
2. A diamond and vertical line in purple indicating your all-time Crickles irregularity ratio. The line makes it easy to situate the value relative to the two boxplots.
3. A label next to the purple diamond giving your relative level based on the this ratio and the underlying statistical model.
4. A blue diamond and vertical line showing your irregularity ratio over the dates chosen in the data range in the sidebar. This defaults to the past six weeks and can be changed so that you can explore how your ratio irregularity ratio has changed over time.
5. An explanatory label next to the blue line/diamond – there is no relative level here akin to that for the all-time ratio.

This report is only available to users who have completed the Crickles survey. If you have completed the survey but see only an empty rectangle on this report it’s likely to be due to you having a high ratio of Check_Strap readings, suggesting that you have strap issues that mean your data may be unreliable in this context and is hence screened out of the analysis. If you haven’t taken the survey yet and do so in future be aware that there may be a delay, potentially of some days, between completing the survey and Irregularity appearing in your menu bar.

The box plot for all Crickles users (as opposed to survey respondents) is not shown but looks similar to the No box plot only with many more outliers at the high end.

There are a number of limitations to this analysis, including the fact that we only have a limited window of history for each subject and this may or may not overlap with any history of arrhythmia. Also there is a significant selection bias in our sample: people who are motivated to take the Crickles survey are more likely to have an arrhythmia diagnosis than the population at large. If you have any questions or observations about your data on the report please do drop us a line.

We would like to publish our methodology for open review in a medical journal with full anonymity of respondent data. This would enable any other parties with a research interest in this topic to examine our workings in detail and thus help us to validate and improve the methodology. To date, Strava have instructed us not to do this using a prohibitory right that they assert in their API agreement. We will continue to petition Strava for their permission to publish, probably in conjunction with an academic partner. Unless and until we secure Strava’s permission, this report is all we can offer.