Germans used to have more Sex in Summer!

DE-monthWow – what a headline … okay, I admit it’s phrased quite sensational given that it anticipates just one possible interpretation of increasingly more births around summer / autumn compared to in spring … but I guess I just get more proactive at marketing with every post I publish!

Okay, enough of that – here’s the deal – essentially looking at the monthly variation of the seasonal component of live births by month reveals strong trends indicating more births in the first half of the year towards the 60s relative to towards 2010 and the opposite relation manifests in the second half. Now assuming a standard duration of labour of 9 months we can calculate the maximum-likelihood month of intercourse – and that’s where it gets juicy! BTW – less children being born in spring means less anxious generations ahead – but more on that later.


For Germany this trend is very strong – June to August becoming less popular for procreation while October to January coming in favour of potential parents.


Estonia shows the same trend pattern, while relative magnitudes between months are different.


Seasonal trend is comparatively week – likely due to the mild climate.


Trend of seasonal pattern reverses at around 1980. According to Google Analytics I had 40 visits from Icelanders in 2014 – my question to you: “What happened?”.

The Data and the Code

Source of the data is Eurostat and specifically the dataset “demo_fmonth“. The decomposition into season, trend and remainder is done using stats::stl() with a seasonal window of 36 months and a trend window of 48 months – I figured this is a good compromise for capturing the seasonal pattern while not diluting it with a too long time span. The code is of course published on GitHub and you can give the code a try right now thanks to devtools::source_url().

And a special biiiig “Thank you very much!” goes to Emmanuel Blondel and Matthieu Stigler for creating rsdmx – which finally makes it a cinch to load SDMX! So far I either had to resort to ill-structured TSVs on Eurostat or use their “SDMX Converter“.

Where’s the Summer Feeling, People?

Now why do for example Germans “make less babies” in summer and instead choose to reproduce in late autumn / winter? I attempt to explain:

  • In earlier days household sizes were larger and hence romantic feelings more likely overcame (future) Mommy and (future) Daddy on a warm sunny day walking through the cornfields!
  • Generation Facebook tends to indulge in hedonistic and narcissistic lifestyle during summer – too busy making selfies … but then autumn strikes – it gets cold and dark and flowers wilk – we start think about getting older and finally dying. A natural reaction is to bring a little copy of yourself into the world!
  • Back in the sixties houses were not so well thermally insulated and equipped with heating systems. Nowadays flats are so warm and so cozy – causing warm and cozy feelings – add candle light and you’re halfway there.
  • Of course procreation got less causally related to intercourse since contraceptives became more available. Which implies that concious decision making gained a more important role.

Any ideas?

The long-term impact on society!

Now hang on to your hat, friend, cause this is not just some harmless time shift of good vibrations … this has long-term and serious impact on society! Scientists published a study indicating that when you are born correlates with five affective temperaments of your future personality [1] [2]. Children born in spring seem to be more anxious than those born in summer/autumn but then again less irritable. More irritable and less anxious is just the right mix of qualities for a career hooligan – that’s bad news!

[1] Season of birth affects your mood later in life (

[2] Association between affective temperaments and season of birth in a general
student population (Journal of Affective Disorders)

Visualized Demographical Data

You are still hungry for more data on life and death – don’t worry, there you go:

(original article published on

4 thoughts on “Germans used to have more Sex in Summer!

  1. Hello Raffael!

    This doesn’t really have anything to do with this particular post but I just thought you might like checking out some of the stuff Nature has recently put out for free for everyone.

    A lot of really cool resources on statistics and some interesting aspects regarding Bayesian statistics ( of which I formally know next to nothing, but it might be something to look out for in the near future). There have been some recent posts about Bayesian stats on R-bloggers, too.

  2. Hi.  Interesting study here.

    I have a stupid question.. the average gestation for women is 280 days – which is actually 10 months not 9 months.  (so if you were pregnant on Jan 1st, you’d deliver on Oct. 7th).   I found that people always refer to 9 months because it is the end of the 9th month that people have a baby.   Did you calculate your study with gestation days or months?

    • Hi Laurie,
      thanks for your (certainly not stupid) question. I think I use the same calculation as you – I’d just refer to your example as 9.25 (approx 9) month of pregnancy or giving birth in the tenth month after intercourse. But what I am now wondering about is how long it takes on average for a woman to become pregnant after intercourse … never thought about that!

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