My website`s bounce rates suddenly dropped to 3.5% & 15% from over 80%

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Farhan Fawzer: A couple of our website's bounce rates suddenly dropped to 3.5% & 15% from over 80%. It began on the 22nd August on one website and other in early September. We didn't make any changes to the website but added a few new blog posts. Just want to know if anyone experiences the same pattern in change of bounce rate or is it only me.
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  Federico Sasso: First thing I'd check is whether Analytics is properly set. Such a huge drop in CR usually is false positive consequent of having Analytics tracking code twice in your html.
  
  I normally see this happens for example when people switches from synchronous to asynchronous code, but forget to remove the old snippet.
  
  Two calls to the scripts, and CR would result a flat zero, except for a small percentage of cases where one doesn't fire (usually the asynch one), normally 3-4% of the cases.
  
  This would very likely explain your 3.5% case. The 15% case is probably another matter.
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  ?ukasz Rogala: Are you tracking outbound links?
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  Farhan Fawzer: +Federico Sasso ;We have replaced the old one with the new Universal Analytics end of July and uses only one set of the script.
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  Farhan Fawzer: +Łukasz Rogala ;Not many outbound links we have.
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  ?ukasz Rogala: But when you track outbound links it's not counted as bounce rate when user clicks on it. So that can be a reason of lowering your bounce rate
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  Edwin Jonk: From the expert panel in this weeks SEO Questions hangout on air on 01:07:11 into the YouTube video: https://dumbseoquestions.com/q/my_websites_bounce_rates_suddenly_dropped_to_35_15_from_over_80 +Farhan Fawzer
  
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  Federico Sasso: LOL I just realized I kept writing CR, while I meant BR (Bounce Rate)
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  Farhan Fawzer: Haha yeah in fact I was wondering for a second but then I guessed might have been a typo. ;
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  Ryan Oscar: What about the traffic sources? And the pages that they are landing on. It's a big drop TBH, so it's hard to think of a reason, especially when you've already stated that you haven't made any chances. Was there a drop in the overall visitors as well?
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  David Kutcher: I'd recheck your site by viewing the outputted source code of your homepage. Then search it for "ua-". If you find more than one result it's because you have two installations of analytics.
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  Farhan Fawzer: +David Kutcher ;Thanks, GA code is not duplicated.
  +Ryan Oscar ;Yes it is a big drop, nothing unusual with landing pages.In fact overall visits from organic improved and had 4500 visits during the month.