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WesPegden's profile
Wes Pegden
Wes Pegden
Wes Pegden
@WesPegden

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Wes Pegden

@WesPegden

Mathematician, CMU.

Pittsburgh, PA, USA
math.cmu.edu/~wes
Joined March 2020

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    1. Wes Pegden‏ @WesPegden 14 Jan 2021

      Wes Pegden Retweeted Wes Pegden

      This thread from December pointed out that convenience samples are not suitable for any but the coarsest estimates of prevalence, and that the popularity of a prevalence study like this can be driven more by its status as an outlier than by its quality. 1/https://twitter.com/WesPegden/status/1336801382955933697 …

      Wes Pegden added,

      Wes Pegden @WesPegden
      The following study is being widely shared as definitive evidence that 76% of the population of Manaus, Brazil, became infected with COVID-19. Quick thread on placing this study in the proper context (and why outliers are so popular...) 1/🧵 https://science.sciencemag.org/content/early/2020/12/07/science.abe9728 …
      Show this thread
      5 replies 34 retweets 118 likes
      Show this thread
    2. Wes Pegden‏ @WesPegden 14 Jan 2021

      At the time I did not give specific examples of confounders one might expect using blood donors (because I wasn't sure what the important ones would be!). 2/

      1 reply 3 retweets 29 likes
      Show this thread
      Wes Pegden‏ @WesPegden 14 Jan 2021

      Later, though, this piece was published, quoting a local epidemiologist pointing out that *free COVID testing was offered as an incentive for donation* (h/t @therealrthorat). This is a very problematic confounder which is not discussed in the paper. 3/ https://www.the-scientist.com/news-opinion/study-estimates-76-percent-of-brazilian-city-exposed-to-sars-cov-2-68272 …pic.twitter.com/Et4AMdr13q

      7:41 PM - 14 Jan 2021
      • 25 Retweets
      • 116 Likes
      • Tim Triche, Jr. Information Junkie 👨‍💻 stag “I AM ESPORTS” runner Sam Becker Kasper Planeta Kepp very special episode Tak beegarc.4freedom Maples "I just follow orders" won't protect you 🌸
      8 replies 25 retweets 116 likes
        1. New conversation
        2. Wes Pegden‏ @WesPegden 14 Jan 2021

          Inferring causation from correlation or prevalence from nonrandom samples is inherently fraught regardless of whether we can correctly guess at specific possible confounders. This example shows the ways in which our imagination can fail. This piece has another lesson also: 4/

          1 reply 7 retweets 47 likes
          Show this thread
        3. Wes Pegden‏ @WesPegden 14 Jan 2021

          The popularity of the study (a prevalence study on blood donors published in Science!) certainly seemed tied to its role in debates about HITs and attack rates. It might be easy to see the study as being in service of a noble cause in an important dispute. 5/

          1 reply 3 retweets 31 likes
          Show this thread
        4. Wes Pegden‏ @WesPegden 14 Jan 2021

          But locally, in Manaus, the study had exactly the opposite effect; local epidemiologists there blame the study for contributing to misplaced optimism about herd immunity from the first wave of the epidemic, and making the case for further pandemic response more difficult. 6/

          2 replies 8 retweets 74 likes
          Show this thread
        5. Wes Pegden‏ @WesPegden 14 Jan 2021

          So much science in the pandemic has been filtered through the lens of preconceived notions about effects on policy. But scientists have not been good at this. It may be better to stick to just trying to understand the truth as well as possible. 7/7

          4 replies 13 retweets 107 likes
          Show this thread
        6. End of conversation
        1. Jon L‏ @JonL8675309 14 Jan 2021
          Replying to @WesPegden @therealrthorat

          Jon L Retweeted Wes Pegden

          JUST incredible...https://twitter.com/WesPegden/status/1349924706586124294?s=20 …

          Jon L added,

          Wes Pegden @WesPegden
          Later, though, this piece was published, quoting a local epidemiologist pointing out that *free COVID testing was offered as an incentive for donation* (h/t @therealrthorat). This is a very problematic confounder which is not discussed in the paper. 3/ https://www.the-scientist.com/news-opinion/study-estimates-76-percent-of-brazilian-city-exposed-to-sars-cov-2-68272 … pic.twitter.com/Et4AMdr13q
          Show this thread
          0 replies 0 retweets 5 likes
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        1. Jon L‏ @JonL8675309 14 Jan 2021
          Replying to @WesPegden @therealrthorat

          Jon L Retweeted Wes Pegden

          "not discussed in the paper" wildhttps://twitter.com/WesPegden/status/1349924706586124294 …

          Jon L added,

          Wes Pegden @WesPegden
          Later, though, this piece was published, quoting a local epidemiologist pointing out that *free COVID testing was offered as an incentive for donation* (h/t @therealrthorat). This is a very problematic confounder which is not discussed in the paper. 3/ https://www.the-scientist.com/news-opinion/study-estimates-76-percent-of-brazilian-city-exposed-to-sars-cov-2-68272 … pic.twitter.com/Et4AMdr13q
          Show this thread
          0 replies 0 retweets 7 likes
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        1. Ryan Horath‏ @therealrthorat 14 Jan 2021
          Replying to @WesPegden

          Thanks Wes. Important thread. I didn't find this out until recently and I was like WHAT!?! It was obvious there were problems because it was so much higher than the other random sample and just so much higher than anywhere else. Age adjusted IFR estimate didn't match, either.

          0 replies 0 retweets 3 likes
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        1. New conversation
        2. Veronica Cristina‏ @veronicacris 14 Jan 2021
          Replying to @WesPegden @therealrthorat

          It doesn't matter a lot because a new strain mutated, so don't dream of herd immunity

          1 reply 0 retweets 0 likes
        3. Show replies
        1. New conversation
        2. Youyang Gu‏ @youyanggu 14 Jan 2021
          Replying to @WesPegden @therealrthorat

          I’m curious how this is different than other randomized seroprevalence studies that basically offer free antibody tests (or in some cases, gift cards upon completion).

          1 reply 1 retweet 4 likes
        3. Wes Pegden‏ @WesPegden 14 Jan 2021
          Replying to @youyanggu @therealrthorat

          I don't know if you're referring to something specific, but in a well-designed random study you would know the response rate, and thus could bound the the effects, e.g., of any incentives on the choice to participate.

          2 replies 0 retweets 9 likes
        4. Show replies

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