Skip to content
By using Twitter’s services you agree to our Cookies Use. We and our partners operate globally and use cookies, including for analytics, personalisation, and ads.
  • Home Home Home, current page.
  • About

Saved searches

  • Remove
  • In this conversation
    Verified accountProtected Tweets @
Suggested users
  • Verified accountProtected Tweets @
  • Verified accountProtected Tweets @
  • Language: English
    • Bahasa Indonesia
    • Bahasa Melayu
    • Català
    • Čeština
    • Dansk
    • Deutsch
    • English UK
    • Español
    • Filipino
    • Français
    • Hrvatski
    • Italiano
    • Magyar
    • Nederlands
    • Norsk
    • Polski
    • Português
    • Română
    • Slovenčina
    • Suomi
    • Svenska
    • Tiếng Việt
    • Türkçe
    • Ελληνικά
    • Български език
    • Русский
    • Српски
    • Українська мова
    • עִבְרִית
    • العربية
    • فارسی
    • मराठी
    • हिन्दी
    • বাংলা
    • ગુજરાતી
    • தமிழ்
    • ಕನ್ನಡ
    • ภาษาไทย
    • 한국어
    • 日本語
    • 简体中文
    • 繁體中文
  • Have an account? Log in
    Have an account?
    · Forgot password?

    New to Twitter?
    Sign up
GidMK's profile
Health Nerd
Health Nerd
Health Nerd
Verified account
@GidMK

Tweets

Health NerdVerified account

@GidMK

Epidemiologist. Writer (Guardian, Observer etc). "Well known research trouble-maker". PhDing at @UoW Host of @senscipod Email gidmk.healthnerd@gmail.com he/him

Sydney, New South Wales
theguardian.com/profile/gideon…
Joined November 2015

Tweets

  • © 2021 Twitter
  • About
  • Help Center
  • Terms
  • Privacy policy
  • Cookies
  • Ads info
Dismiss
Previous
Next

Go to a person's profile

Saved searches

  • Remove
  • In this conversation
    Verified accountProtected Tweets @
Suggested users
  • Verified accountProtected Tweets @
  • Verified accountProtected Tweets @

Promote this Tweet

Block

  • Tweet with a location

    You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more

    Your lists

    Create a new list


    Under 100 characters, optional

    Privacy

    Copy link to Tweet

    Embed this Tweet

    Embed this Video

    Add this Tweet to your website by copying the code below. Learn more

    Add this video to your website by copying the code below. Learn more

    Hmm, there was a problem reaching the server.

    By embedding Twitter content in your website or app, you are agreeing to the Twitter Developer Agreement and Developer Policy.

    Preview

    Why you're seeing this ad

    Log in to Twitter

    · Forgot password?
    Don't have an account? Sign up »

    Sign up for Twitter

    Not on Twitter? Sign up, tune into the things you care about, and get updates as they happen.

    Sign up
    Have an account? Log in »

    Two-way (sending and receiving) short codes:

    Country Code For customers of
    United States 40404 (any)
    Canada 21212 (any)
    United Kingdom 86444 Vodafone, Orange, 3, O2
    Brazil 40404 Nextel, TIM
    Haiti 40404 Digicel, Voila
    Ireland 51210 Vodafone, O2
    India 53000 Bharti Airtel, Videocon, Reliance
    Indonesia 89887 AXIS, 3, Telkomsel, Indosat, XL Axiata
    Italy 4880804 Wind
    3424486444 Vodafone
    » See SMS short codes for other countries

    Confirmation

     

    Welcome home!

    This timeline is where you’ll spend most of your time, getting instant updates about what matters to you.

    Tweets not working for you?

    Hover over the profile pic and click the Following button to unfollow any account.

    Say a lot with a little

    When you see a Tweet you love, tap the heart — it lets the person who wrote it know you shared the love.

    Spread the word

    The fastest way to share someone else’s Tweet with your followers is with a Retweet. Tap the icon to send it instantly.

    Join the conversation

    Add your thoughts about any Tweet with a Reply. Find a topic you’re passionate about, and jump right in.

    Learn the latest

    Get instant insight into what people are talking about now.

    Get more of what you love

    Follow more accounts to get instant updates about topics you care about.

    Find what's happening

    See the latest conversations about any topic instantly.

    Never miss a Moment

    Catch up instantly on the best stories happening as they unfold.

    Health Nerd‏Verified account @GidMK 6 Jun 2018

    There's been a lot of controversy about drug sniffing dogs. Here's why they are totally useless as an intervention (thread)

    5:38 PM - 6 Jun 2018
    • 7 Retweets
    • 19 Likes
    • Mikael R.S. Lake Emma_Archer Synaptically Yours, EtC Andrew Fermor gen x elder nurse nette Martin Tomko Nick Evershed Wendy Wilkinson 🙀🐱🐈🦘
    5 replies 7 retweets 19 likes
      1. New conversation
      2. Health Nerd‏Verified account @GidMK 6 Jun 2018

        We want to know how accurate a test sniffer dogs are. To put it another way: what are the rates of true positives and true negatives when we test people with sniffer dogs?

        1 reply 1 retweet 2 likes
        Show this thread
      3. Health Nerd‏Verified account @GidMK 6 Jun 2018

        According to the police, the true positive rate for sniffer dogs is 80% - there is a 4 in 5 chance that an alert from a dog will result in the person having drugs or having recently been in contact with drugspic.twitter.com/4S004hPJwZ

        1 reply 1 retweet 1 like
        Show this thread
      4. Health Nerd‏Verified account @GidMK 6 Jun 2018

        So what's the true negative rate i.e. the chance that someone who DOESN'T get stopped DOES have drugs?

        1 reply 1 retweet 3 likes
        Show this thread
      5. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Well, this is extremely hard to know. Some research suggests it is close to 0% (!), because huge numbers of people get into music festivals with drugs But let's assume it's better, maybe at the same 80% figure we're using abovepic.twitter.com/BzKXWM1nBl

        1 reply 1 retweet 2 likes
        Show this thread
      6. Health Nerd‏Verified account @GidMK 6 Jun 2018

        So let's say that 100 people turn up to a music festival. Of these, 5 have drugs on them and 10 have recently been in contact with drugs

        1 reply 1 retweet 1 like
        Show this thread
      7. Health Nerd‏Verified account @GidMK 6 Jun 2018

        For this type of test, we usually make a 4x4 grid to represent the rates of true and false positives, like so we can fill in the numbers at the end of the right straight uppic.twitter.com/RnDHZ9Ormf

        1 reply 1 retweet 1 like
        Show this thread
      8. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Now, our true positive rate - taken from the police - is 80%. That means that out of our 15 "has drugs" people, we'll identify 15*0.8 = 12 correctly, and 15*0.2 = 3 incorrectly, like sopic.twitter.com/e2SFzTJ6aY

        1 reply 1 retweet 1 like
        Show this thread
      9. Health Nerd‏Verified account @GidMK 6 Jun 2018

        So far, all well and good. Lots of people correctly identified, not that many missed. Very few "false negatives" But wait, there's more

        2 replies 1 retweet 1 like
        Show this thread
      10. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Now, let's apply our "true negative" rate. We're assuming that the test is 80% accurate at identifying people who don't meet our criteria. So 85*0.8 = 68 correctly identified and 85*0.2 = 17 incorrectly identified This doesn't look so good!pic.twitter.com/s3dZwKWfbp

        1 reply 1 retweet 1 like
        Show this thread
      11. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Overall, the total number of people who test "positive" is 17+12 = 29, and the total "negative" is 3+68 = 71pic.twitter.com/LONF7eVjyI

        1 reply 1 retweet 2 likes
        Show this thread
      12. Health Nerd‏Verified account @GidMK 6 Jun 2018

        So using our (ENORMOUSLY GENEROUS - I'll get to this in a second) assumptions, the predictive value of the dogs is around 40%

        1 reply 1 retweet 2 likes
        Show this thread
      13. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Health Nerd Retweeted Health Nerd

        This gives you some idea of the issue - for every 100 people screened by sniffer dogs, a large volume of people will be found to have drugs who don'thttps://twitter.com/GidMK/status/1004527525551173632 …

        Health Nerd added,

        Health NerdVerified account @GidMK
        So using our (ENORMOUSLY GENEROUS - I'll get to this in a second) assumptions, the predictive value of the dogs is around 40%
        Show this thread
        1 reply 1 retweet 1 like
        Show this thread
      14. Health Nerd‏Verified account @GidMK 6 Jun 2018

        In fact, even if sniffer dogs are right 80% of the time, because taking drugs is less common than not taking drugs, you'll catch more INNOCENT people than guilty ones

        1 reply 1 retweet 2 likes
        Show this thread
      15. Health Nerd‏Verified account @GidMK 6 Jun 2018

        But...what if the dogs aren't right that much? What if, as many people argue, the dogs are wrong 50% of the time? Or 75%?

        1 reply 1 retweet 1 like
        Show this thread
      16. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Here's where it gets really problematic. Here's the table where the dogs are right 80% of the timepic.twitter.com/6IB2Jpy4KW

        1 reply 1 retweet 4 likes
        Show this thread
      17. Health Nerd‏Verified account @GidMK 6 Jun 2018

        And here are the tables for 50% and 25% - both of which have been observed in real lifepic.twitter.com/yOYKVtyggW

        1 reply 1 retweet 3 likes
        Show this thread
      18. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Health Nerd Retweeted Health Nerd

        As you can see, the predictive power goes down significantly. Even with 50% accuracy, only 1 in 5 of the people stopped will actually have drugs on themhttps://twitter.com/GidMK/status/1004530137872809984 …

        Health Nerd added,

        Health NerdVerified account @GidMK
        And here are the tables for 50% and 25% - both of which have been observed in real life pic.twitter.com/yOYKVtyggW
        Show this thread
        1 reply 1 retweet 2 likes
        Show this thread
      19. Health Nerd‏Verified account @GidMK 6 Jun 2018

        This is why when you are testing for an uncommon outcome, your test has to be REALLY GOOD Drug sniffing dogs, even by the best estimates, are not

        1 reply 1 retweet 2 likes
        Show this thread
      20. Health Nerd‏Verified account @GidMK 6 Jun 2018

        This goes doubly for screening large numbers of people. If you screen, say, everyone who goes into a music festival, you will likely catch few offenders but identify many totally innocent people

        2 replies 1 retweet 1 like
        Show this thread
      21. Health Nerd‏Verified account @GidMK 6 Jun 2018

        So what should we do to prevent harm from drugs if we know sniffer dogs are ineffective? Tons of things. I'll make another thread about these options if anyone's interested

        1 reply 0 retweets 1 like
        Show this thread
      22. Health Nerd‏Verified account @GidMK 6 Jun 2018

        Also P.S. I got a few pieces of terminology wrong - in particular, the first tweet should read "diagnostic test" not "intervention" - and also the "25% table" is slightly misleading as I've assumed that the negative predictive power is still 75% rather than 25%

        1 reply 0 retweets 1 like
        Show this thread
      23. Health Nerd‏Verified account @GidMK 6 Jun 2018

        P.P.S TL:DR version is that drug sniffer dogs, even when they get it right 80% of the time, still make more mistakes than "hits" when not that many people have drugs

        0 replies 0 retweets 1 like
        Show this thread
      24. End of conversation

    Loading seems to be taking a while.

    Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.

      Promoted Tweet

      false

      • © 2021 Twitter
      • About
      • Help Center
      • Terms
      • Privacy policy
      • Cookies
      • Ads info