1. Rory

    Rory Senior Member

    Often described as an old wives' tale, the idea of a connection between the phase of the moon and an increase in birth rates still persists today, including among those who work in childbirth, as exemplified in this article at The Huffington Post:
    While some early studies appeared to support the idea, later large scale analyses - one looking at over half a million births - found no correlation between birth dates and any particular phase of the moon.

    The study using the largest amount of data, however - some 50 millons births - did propose a correlation, concluding that:
    Despite contradicting other analyses, as well as scientific understanding, given that the source of the study was the Astrophysics Department at Appalachian State University, it seemed worth looking at again. So...

    I downloaded 21 years worth of daily birth data, totalling some 89.5 million births, and plotted this against the phase of the moon. While I didn't think it strictly necessary, Caton and Wheatley had performed some data cleansing to eradicate anomalies such as weekends and holidays (substantially lower rates) and Tuesdays (higher rates), so I did this as well (as expected, with such a huge supply of data over a large timescale, it made no significant difference).

    These are the results:

    upload_2018-12-5_0-32-4. upload_2018-12-4_21-57-28.
    Key: Day 0=new moon; average births per day excluding weekends, holidays and Tuesdays; 13500/+1 in chart=full moon, 11500/-1=new moon; second chart repeats to better represent the lunar cycle

    Some conclusions:
    • There is no pattern or correlation with the lunar cycle
    • The largest daily variation from average is only 0.74%
    • The majority of points lie less than 0.21% from average
    • There is no significant increase or decrease in any phase of the moon
    • Births on the full moon, and in the three-day period around the full moon, are almost exactly average (-0.03 and +0.14% respectively)
    • There are no 'peak' or 'minimum' birth rates, just very slight random variations, as would be expected
    This, I believe, is the largest analysis to date on the subject, and, I would imagine, pretty conclusive.

    If anything further were needed, though, I did find - after completing everything - that Caton and Wheatley had followed up their earlier paper and run an improved model using data for around 70 million births.

    This time they found no correlation.
    Last edited: Dec 4, 2018
  2. deirdre

    deirdre Moderator Staff Member

    why do you have 34 pink points on your chart? and since you still have 29 days in your left hand side, what kind of 'cleansing' did you do? also where did you get your initial data from?
  3. Rory

    Rory Senior Member

    Good questions. :)

    1. Because the lunar cycle is a cycle, the chart is slightly repeated, to better represent it (I should probably mention that)
    2. What's been removed are Tuesdays, weekends, and holidays. The way this works is: let's say there are 7670 data points - i.e., individual day records - then once the aforementioned are removed, we're left with about 4000. This equals to about 140 daily records for each day of the lunar cycle. It's not days of the lunar cycle that are removed, but rather occasional daily records. This removal doesn't affect the final results, in the sense of altering the relationship of one day of the cycle to another, given that they're averages. And, as I mentioned above, the same general result is shown whether these are included or not: there are just so many records and data points that each day of the lunar cycle will fall on more or less the same number of weekends, holidays, and Tuesdays.
    3. There's a link above. That says it's from the Centers for Disease Control and Prevention's National Center for Health Statistics.

    I'll attach my spreadsheet if anyone wants a peruse. Probably a bit higgledy-piggledy in places, but it should make sense.

    Attached Files:

  4. deirdre

    deirdre Moderator Staff Member

    oh i see. you just mirrored it for some reason.

    then why are there 29 days on the left hand chart?

    ok. you went through both those pages and manual added all the days for each day of every year then averaged them? while simultaneously correlating which is a weekend, sunday and tuesday?
  5. deirdre

    deirdre Moderator Staff Member

    what? its 21 years of data. so there shoul dbe 21 daily records for each day of the lunar cycle.
  6. Rory

    Rory Senior Member

    I might be misunderstanding your question, but are you thinking that because there are no Tuesdays in the data - forgetting holidays and weekends for the time being - that there should be one (or more) less days in the left-hand column?

    If so, the answer is because over the course of 21 years there will be around 260 lunar cycles. Each day of the lunar cycle will occur 260 times and 'collect' 260 points of data. The spread of the week is even. Remove Tuesdays and you remove 260/7 data points. That leaves 223 data points. When holidays and weekends are similarly removed that leaves around 140 data points.

    Even with so many removed, this still generates around 1.83 million live births for each day of the lunar cycle.

    Here's a chart to show the difference removing each 'significant variable' makes:


    The reason it doesn't change the overall picture is because all the variables - weekends, holidays, and Tuesdays - will be averaged out over the lunar cycle, so that each day receives its 'fair share'. On the micro level, the picture may change a little, but overall each day remains within touching distance of the average - that is, whichever way we look at it, there are no significant peaks, troughs, or variations.

    Hope that helps to clarify. :)
    Last edited: Dec 4, 2018
  7. deirdre

    deirdre Moderator Staff Member

    sorry. i wasnt thinking those were days of the lunar cycle (even though i see now it says 'cycle). i forgot the moon changes calender days. airhead moment.
    • Like Like x 1
  8. deirdre

    deirdre Moderator Staff Member

    that's what i was thinking. why remove or 'normalize' them at all.
  9. Rory

    Rory Senior Member

    It makes sense if you only have a small data set, as some entries may correspond with a higher number of 'outliers' than others, and that would throw it off. But on something this massive it doesn't make any significant difference.
    • Like Like x 1
  10. Rory

    Rory Senior Member

    Been looking at this again, just to make sure I'd done everything right, and I can see a few places for improvement.

    Number one, I've figured a much better way of calculating the lunar cycle, including one way which factors in for 'Day 29', which only 'appears' half the time.

    Mainly, though, it's with regard to the 'normalization' - I was totally wrong about that, and it doesn't 'average out', even over 21 years and 260 lunar cycles. Some 'lunar days', then, fall much more often, or more seldomly, on low birthrate days such as holidays, weekends, Mondays, etc, and it makes a massive difference: Day 21 after a full moon, for example, returns 173,000 more births than Day 22 when Mondays are excluded.

    It was quite striking till I tallied up and found that Day 22 fell on 4 less Mondays than Day 21, while Day 21 landed on four Tuesdays, the most popular day.

    The spreads are as follows:
    • Mondays and Tuesdays - minimum 34, maximum 39
    • Weekend days - 71 to 76
    • 13th of the month - 4 to 12
    • Holidays - 3 to 13
    • Non-weekend holidays - 1 to 9
    • Valentines Day - 0 to 2 (higher birthrate)
    Caton and Wheatley also suggested factoring in for seasonal variations. Broadly speaking, there are two 'seasons' for birth rates:
    • June-October - with a spread of 108 to 110
    • November-May - 149 to 152
    Seasonal variations seem to be less of a factor than holidays, etc. Tuesdays, also, though the most popular day, are not so much at variance as Mondays - Tuesdays are +2% on Tue-Fri, while Mondays are 8% down. Probably due to more holidays falling on a Monday, as well as 'long weekends'.

    'Normalization', then, looks rather tricky. But probably I'll have a go at a big long equation to give it the best shot. And still prove the same thing as was shown in the beginning. ;)

    (Spreadsheet attached)

    Attached Files:

  11. Rory

    Rory Senior Member

    It sure makes me think how important it is to go through stats with a fine toothcomb. Sneaky anomalies are waiting around every corner. :)
  12. Rory

    Rory Senior Member

    Strangely, two studies on a possible correlation between the lunar cycle and birth rates were published within a few months of each other in 2016 - only this time involving cows.

    One study was carried out by Professor Tomohiro Yonezawa of the University of Tokyo, and quite widely reported on, at places like Live Science, Agriland (Ireland), ABC Australia, Asian Scientist, and, of course, The Daily Mail.
    Good university. Smart professor. Very low probability of chance. Looks convincing, right?

    Except...they only studied birth records for 428 deliveries.

    I personally find that kind of shocking, that a presumably reputable establishment such as the University of Tokyo would not only put that out, but think there might be something in it in the first place.

    The other study, meanwhile, published a few months earlier, looked at records involving over two million births and found no correlation with any particular day or phase of the lunar cycle:
    This study, however, seems to have received little or no press.

    Correction: that should read "Day 21 landed on four more Tuesdays."
    Last edited: Dec 8, 2018 at 1:26 AM
  13. Rory

    Rory Senior Member

    I'm having a go at the normalization - and it's definitely more intricate than would first appear, what with birth rates changing depending on which day of the week holidays fall on, days surrounding holidays receiving a boost, and even whether particular days happen to randomly coincide more often with fallow or productive years.

    Checking for anomalies revealed one interesting non-holiday that needs normalizing - post-2001 September 11th:


    This chart shows the difference in average daily birthrate for each of the above dates compared to the September weekday average. Before 9/11, the 11th was an almost exactly average day - now, it's about 6% down, and even less popular than Friday the 13th.

    I'm not sure if this has been confirmed before, but a 2013 analysis and anecdotal evidence suggested as much.