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GidMK's profile
Health Nerd
Health Nerd
Health Nerd
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@GidMK

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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

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    1. Health Nerd‏Verified account @GidMK 23 Jan 2020

      So, what did the scientists do? Well, on first blush it looks like they did a simple cohort study - took a group of people, split them up by whether they were exposed to cats/dogs, and compared their mental health years laterpic.twitter.com/QzofRQIDQm

      1 reply 0 retweets 3 likes
      Show this thread
    2. Health Nerd‏Verified account @GidMK 23 Jan 2020

      But then you look a little closer, and you realize that this is actually a CASE-CONTROL study, because the authors selected their patients based on outcomes (mental health diagnosis), not exposure (having pets)pic.twitter.com/DSqVa6SVLF

      1 reply 0 retweets 10 likes
      Show this thread
    3. Health Nerd‏Verified account @GidMK 23 Jan 2020

      (Tip for non-epi people: the difference between a case-control and cohort can be hard to get at first, but just look at how they selected their participants. If they picked people based on their outcomes, it's case-control)

      2 replies 0 retweets 7 likes
      Show this thread
    4. Health Nerd‏Verified account @GidMK 23 Jan 2020

      Ok, so it's a case-control being reported as a cohort study That's a problem, maybe, but not that much Let's look at the resultspic.twitter.com/0UWqXnAYrn

      1 reply 0 retweets 2 likes
      Show this thread
    5. Health Nerd‏Verified account @GidMK 23 Jan 2020

      And this is where things get really, REALLY weird Compare this sentence in the results to the graph. Notice anything strange here?pic.twitter.com/gPsfY11Oa6

      1 reply 0 retweets 3 likes
      Show this thread
    6. Health Nerd‏Verified account @GidMK 23 Jan 2020

      (Note: I'm not talking about how they used cross-sectional data to fudge longitudinal analyses. We'll get to that)

      1 reply 0 retweets 2 likes
      Show this thread
    7. Health Nerd‏Verified account @GidMK 23 Jan 2020

      The sentence I highlighted above is just...wrong If that's the analysis they did, then they didn't show that "the time of the first household pet dog...was associated with a significantly decreased hazard of having a schizophrenia diagnosis"

      1 reply 0 retweets 3 likes
      Show this thread
    8. Health Nerd‏Verified account @GidMK 23 Jan 2020

      This graph shows a Kaplan-Meier curve plotting the proportion who got a dog against the age that they reported getting one, by group It's testing whether people who are currently diagnosed with SP or BPD were more likely to get a dog as a child!pic.twitter.com/8TpWFUdsz3

      1 reply 0 retweets 6 likes
      Show this thread
    9. Health Nerd‏Verified account @GidMK 23 Jan 2020

      In other words, the main finding of this paper, the one reported everywhere, is NOT that dogs reduce your risk of schizophrenia, it's that schizophrenia reduces your risk of dogs!pic.twitter.com/F3Bd14tNLP

      1 reply 2 retweets 25 likes
      Show this thread
    10. Health Nerd‏Verified account @GidMK 23 Jan 2020

      Now, it's not the fault of the media that this was reported wrong - it's wrong IN THE PAPER This is perhaps not surprising, because there are quite a few other mistakes...

      1 reply 0 retweets 4 likes
      Show this thread
      Health Nerd‏Verified account @GidMK 23 Jan 2020

      This sentence is statistically weird. If you're correcting for multiple comparisons (good) you can't just undo that by using the 'trend'pic.twitter.com/AiaTknBffm

      1:50 PM - 23 Jan 2020
      • 1 Like
      • Alan B. Holloway
      1 reply 0 retweets 1 like
        1. New conversation
        2. Health Nerd‏Verified account @GidMK 23 Jan 2020

          The authors also report 'relative risks' even though they used logistic models You ~can~ convert the results of a logistic model to a relative risk, but it's not that easy and they didn't report doing so, which means the RRs are probably just ORspic.twitter.com/OB1QLZ7jJA

          1 reply 0 retweets 5 likes
          Show this thread
        3. Health Nerd‏Verified account @GidMK 23 Jan 2020

          Health Nerd Retweeted Health Nerd

          But all of this pales in comparison to the massive issue I skipped past earlier The study used longitudinal analysis (Cox/KM) to analyze cross-sectional datahttps://twitter.com/GidMK/status/1220462617472487425?s=20 …

          Health Nerd added,

          Health NerdVerified account @GidMK
          (Note: I'm not talking about how they used cross-sectional data to fudge longitudinal analyses. We'll get to that)
          Show this thread
          1 reply 0 retweets 2 likes
          Show this thread
        4. Health Nerd‏Verified account @GidMK 23 Jan 2020

          You'd think from the results that they had monitored children over time, recorded when they got a pet, and then followed up years later to find out if they got a diagnosis But remember - this is a CASE-CONTROL study

          1 reply 0 retweets 4 likes
          Show this thread
        5. Health Nerd‏Verified account @GidMK 23 Jan 2020

          What the authors actually did is ASK PEOPLE WITH A CURRENT DIAGNOSIS when they remembered getting a dog as a child This is an inherently flawed approachpic.twitter.com/Kwo4i0guDD

          1 reply 1 retweet 7 likes
          Show this thread
        6. Health Nerd‏Verified account @GidMK 23 Jan 2020

          Imagine asking someone who is currently going through an inpatient admission for acute psychosis when they remember getting a dog as a child, and using that as your exposure variable You see the problem

          1 reply 0 retweets 12 likes
          Show this thread
        7. Health Nerd‏Verified account @GidMK 23 Jan 2020

          So this study didn't even really measure whether people who were diagnosed with schizophrenia were more likely to get dogs as children It measured who was more likely to REMEMBER getting a dog as a childpic.twitter.com/9wIOr6YxN0

          1 reply 0 retweets 11 likes
          Show this thread
        8. Health Nerd‏Verified account @GidMK 23 Jan 2020

          And using the time that they remembered having a dog as the time-point for a longitudinal analysis is...problematic For one thing, you don't have accurate pet death data. You don't actually know how long these people were exposed to pets!

          1 reply 0 retweets 4 likes
          Show this thread
        9. Health Nerd‏Verified account @GidMK 23 Jan 2020

          I'm going to stop here, because while there's more there really isn't much point in going through it allpic.twitter.com/9ZPrh2WLfs

          1 reply 0 retweets 7 likes
          Show this thread
        10. Health Nerd‏Verified account @GidMK 23 Jan 2020

          The fact that the analyses were the wrong way around, the exposure was a bit meaningless, and that the stats were probably misreported is probably enough And yet, the study was published, and got into the NYT *sigh*

          1 reply 0 retweets 6 likes
          Show this thread
        11. Health Nerd‏Verified account @GidMK 23 Jan 2020

          TL:DR - dogs don't prevent schizophrenia - schizophrenia may prevent dogs - even then, probably not - this study is a mess

          4 replies 3 retweets 31 likes
          Show this thread
        12. Health Nerd‏Verified account @GidMK 23 Jan 2020

          Health Nerd Retweeted Darren Dahly, PhD

          If you want more info, @statsepi and @ADAlthousePhD explain really well in this thread:https://twitter.com/statsepi/status/1220015078726098944?s=20 …

          Health Nerd added,

          Darren Dahly, PhD @statsepi
          I got 100 bucks for anyone from @jhubiostat that can explain what was actually done in this paper! 😜 #statstwitter https://twitter.com/JohnsHopkinsSPH/status/1220003201165996033 …
          Show this thread
          1 reply 0 retweets 3 likes
          Show this thread
        13. End of conversation

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