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How not to die when watching television Sometime last week the British, and probably international, newspapers were full of stories about  these new scientific data proving that binge watching (i.e. watching more than one episode  of a series at a time, suppose) is detrimental to your health. Just a selection of the headings: “Binge watching TV can actually kill you, study finds” (Independent) “Why binge watching your TV box-sets could kill you”(Telegraph)  “Binge watching TV programmes could kill you, according to Japanese scientists” (BBC)  “Netflix and kill warning as watching too much telly can increase risk of dying” (Mirror)  Pretty serious stuff... So it seems that binge watching ‘Orange is the new Black’, for example, can directly kill  you through a pulmonary embolism (a blood clot stuck in the wrong place in the lung  (wiki)). Anyway, that sounds a bit excessive, so I thought I’d have a look at the paper and see what  it was all about. It took me a while to find it, but finally: you can find it here too <link>. It  is more of an extended abstract than a paper really, but it gives us the opportunity to look  a bit closer at the numbers.   The main thing to realize, from the start, is that all the newspapers are wrong. I am sure  this is not something new to you….you are clever and you know what the tabloids are all  about?! Interestingly, quite a lot of the responsible journalists managed to link the  increased risk of pulmonary embolism to binge watching of boxed DVD sets or of Netflix  series (I don’t the actual series mattered…).The study followed up 86,024 Japanese people  (actually 110,585, but not everyone provided all useful data) from 1988-90 for, on average  19.2 years. Some quick mental arithmetics later and we realize that this means that people  were followed up until 2009 on average (and indeed, the official end of follow-up was end  of 2009)…..and a quick google search reveals Netflix launched in Japan in 2015. So it has  nothing to do with online services. In fact, any of the series worth binge watching are quite  recent…  …of course, you realized ages ago that what the study is really looking at is sedentary  behaviour or, in scientific terms, being a couch potato. The participants were asked to self-report their average time spent watching television in  hours per day. This, let’s face it, is quite difficult to do accurately. I suppose that because  the researchers are aware of this too, they reclassified everyone into 3 categories of  hours/day watching television: less than 2.5 hours, 2.5-4.9 hours, and more than five  hours. The statistical models were also adjusted for some important lifestyle factors (you  know, the usual suspects, smoking and the lot). But seriously !!! More than five hours of watching television…..daily…..on average….. So how bad is it? Looking at the numbers, it is quite bad. For every two hours extra of watching television,  on average, your risk (as a hazard ratio) increases by 40%. In fact, compared to the  reference group who watch television for less than two and a half hours per day on  average, you have a 70% increased risk if you were to watch between 2.5 and 4.9 hours per  day and a 150% increased risk if you watch for more than five hours per day. I mean that  is…..that is…wow….that is dangerous! This seems like a good moment to pause, and breathe, and discuss relative compared to  absolute numbers. There were 86,024 people in the study of which 59 died of pulmonary embolism. That looks  a lot less dangerous; in fact, it is about 1 in every 1,600. Or a 0.07 % chance. So what do these big hazard ratios implying up to 150% increased risks actually mean? The  table in the paper calculates everything by person-years, which makes off-the-cuff  calculations a bit complicated, but just, for the sake of argument, make life a bit easier  since we cannot directly use the number of cases in each category (the number of person  years is different in each group, after all). If we do that, then the mortality rate per  100,000 person-years from the table (2.8,4.8 ,and 8.2 for the different categories) gives us  a total of 15.8. The 59 deaths divided by that 15.8 gives us 3.7 death per rate-unit, from  which we, more or less, get the number of cases if all groups were the same: 10 in the  reference group, 19 in the group that watched television between 2.5 and 4.9 hours per  day, and 30 in the group that watched for more than 5 hours daily (there are other, quick  ways of doing this, which will give you somewhat different numbers, such as just  multiplying the number in the lowest group by the hazard ratio, but give or take you get  the same pattern). With the above, we now know what your actual increase in risk is. As calculated above,  overall it is 1 in every 1,600 people, or 0.07%. With the calculations above this can now be  split out in three equally sized groups, and for those who only watched for less than two  and a half hours daily, this would be 1 in every about 3,000 people, or 0.03% [100*(10  deaths/28,675)]. For those who watched between 2.5 and five hours, this would be 1 in  every 1,500, or 0.07%, and for everyone would be watching television for more than five  hours daily, this would be 1 in every 1 in every 1,000, or 0.10%. So what is there to say about the above? I would say that the risk of dying from a blood clot getting stuck in the wrong place in your  lungs is pretty slim. And despite the 150% increase in risk, it is still pretty slim if you were  to watch more than 5 hours of television daily for the rest of your life. As such, I can see  why, although interesting, this was not published as a full paper. In those kind of terms, the news is really not very dramatic. It also has nothing to do with the act of watching Netflix,  DVD boxes, or watching television specifically. What it does say is that living your life as a couch potato is not such a great idea. I mean,  we already knew that. It is not for the increased risk of pulmonary embolism that this is a  bad idea though, it’s because a sedentary lifestyle is a pretty bad idea with respect to  quite a lot of other health, mental and social harms, all of which are much more frequent  (obesity, heart disease, diabetes, cancer, anxiety, depression, just to name a few). I didn’t make all this up either; NHS Choices for example, also felt compelled to put these  newspaper articles into perspective, and said pretty much the same (link).      
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