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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 Aug 30

      A lot of people in the world of evidence appraisal use the phrase "Garbage-In Garbage-Out" (GIGO) to describe bad meta-analyses I thought I'd briefly explain what this means 1/n

      14 replies 104 retweets 347 likes
      Show this thread
    2. Health Nerd‏Verified account @GidMK Aug 30

      2/n This all comes back to what a meta-analysis *does* In essence, it's very simple. Think of your bog-standard arithmetic mean (average) - a bunch of numbers added together then divided by the totalpic.twitter.com/K4R0jJKbzO

      1 reply 7 retweets 42 likes
      Show this thread
    3. Health Nerd‏Verified account @GidMK Aug 30

      3/n This is the most basic form of meta-analysis - lump all the numbers together into an average. Simple, but obviously flawedpic.twitter.com/tLQTpXSdvz

      1 reply 6 retweets 33 likes
      Show this thread
    4. Health Nerd‏Verified account @GidMK Aug 30

      4/n Let's say you have a study of 10,000 people with a value of 5 for your outcome of interest, and another study with a value of 10 people with a value of 15 The crude average is (5+15)/2 = 10, but that's clearly not useful

      1 reply 6 retweets 34 likes
      Show this thread
    5. Health Nerd‏Verified account @GidMK Aug 30

      5/n So what we do instead is weight the studies This is our meta-analytic model - a *weighted* average that gives more weight to bigger/better studies

      1 reply 6 retweets 39 likes
      Show this thread
    6. Health Nerd‏Verified account @GidMK Aug 30

      6/n A common method of doing this is to use the inverse of the variance of the studies. This essentially uses the confidence intervals of each study as a weighting tool, with tighter intervals getting a higher weightpic.twitter.com/yW7WF1YY8o

      1 reply 8 retweets 43 likes
      Show this thread
    7. Health Nerd‏Verified account @GidMK Aug 30

      7/n Here's an example from the ivermectin literature - this is simply a weighted average where the weighting is derived from the inverse of the variance (calculated from the confidence intervals)pic.twitter.com/ux75gk6HFz

      1 reply 7 retweets 36 likes
      Show this thread
      Health Nerd‏Verified account @GidMK Aug 30

      8/n But you can immediately see the issue here - this weighting is DERIVED FROM THE DATA If the data is unreliable, the weighting is meaningless!pic.twitter.com/7Noojnz1iQ

      10:28 PM - 30 Aug 2021
      • 8 Retweets
      • 71 Likes
      • Kieron Drake the sailing science shill ⛵️ Asha Brunings Wen Dombrowski MD MBA - it's ok to grieve & rest John Alan Garde c0nc0rdance (((Dorit Reiss))) ナオミ
      2 replies 8 retweets 71 likes
        1. New conversation
        2. Health Nerd‏Verified account @GidMK Aug 30

          9/n If I were to, say, fabricate a large trial that had a heavy weight, it would completely mess up the meta-analysis and make the results unreliable For ivermectin, we KNOW that this has happenedhttps://gidmk.medium.com/is-ivermectin-for-covid-19-based-on-fraudulent-research-5cc079278602 …

          4 replies 20 retweets 89 likes
          Show this thread
        3. Health Nerd‏Verified account @GidMK Aug 30

          10/n So this is what we mean by GIGO. If you incorporate bad numbers into a meta-analysis, by definition the results are also bad, because the model is simply an average of the numbers you input 🤷‍♂️

          1 reply 7 retweets 46 likes
          Show this thread
        4. Health Nerd‏Verified account @GidMK Aug 30

          11/n This is why most of the work of meta-analysis is to carefully choose the studies you use, because if your model is based on garbage the results will also be garbage

          1 reply 9 retweets 62 likes
          Show this thread
        5. Health Nerd‏Verified account @GidMK Aug 30

          12/n A good way to think of this for laypeople is to think of a simple, boring average Would you average out the included studies? If not, the meta-analysis probably doesn't make sense

          2 replies 6 retweets 37 likes
          Show this thread
        6. Health Nerd‏Verified account @GidMK Aug 30

          13/n I think the website ivmmeta is actually a brilliant teaching tool for what not to do here. Can you imagine adding up the time it takes for people to recover and the proportion of people who had symptoms and dividing by 2? What would that even mean?pic.twitter.com/Cd9Bg2rWsV

          7 replies 12 retweets 111 likes
          Show this thread
        7. End of conversation
        1. New conversation
        2. Ahmed Alnajar, MD, MSPH‏ @Alnajar_MD Aug 31
          Replying to @GidMK

          How to determine of the study has a reliable data?

          1 reply 0 retweets 0 likes
        3. Health Nerd‏Verified account @GidMK Aug 31
          Replying to @Alnajar_MD

          That's a very complex question! Depends on the study

          0 replies 0 retweets 0 likes
        4. End of conversation

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