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GidMK's profile
Health Nerd
Health Nerd
Health Nerd
Verified account
@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. Josh Ketter‏ @sangfroyd 31 Aug 2020
      Replying to @GidMK

      That's not correct - decay rate was unknown when the sens & spec were provided They are relative to & dependent on the sampling timeframes against the curves Did you examine this? Many studies actually adjust for these. Yours is one of the few who didn't

      1 reply 0 retweets 0 likes
    2. Health Nerd‏Verified account @GidMK 31 Aug 2020
      Replying to @sangfroyd

      I have no idea what you mean by "were provided", we cited a number of very recent studies on exactly this point. I also don't think you've actually understood the point about test sensitivity here

      2 replies 0 retweets 0 likes
    3. Health Nerd‏Verified account @GidMK 31 Aug 2020
      Replying to @GidMK @sangfroyd

      From recent evidence, we know that ELISA sensitivity is ~80% i.e. https://www.bmj.com/content/370/bmj.m2516 … What you're suggesting, as far as I can tell, is that there is an ADDITIONAL element, aside from the 20% false negatives we already know about, that would be missed by the ELISA

      1 reply 0 retweets 1 like
    4. Josh Ketter‏ @sangfroyd 31 Aug 2020
      Replying to @GidMK

      Correct. Obviously depends on the exact test used. But generally it's the % of infections that have decayed by the measurement date, and therefore changes the weighting of decay, similar to how true prev effects PPV. This is relative to each community & their point on curve

      1 reply 0 retweets 0 likes
    5. Health Nerd‏Verified account @GidMK 31 Aug 2020
      Replying to @sangfroyd

      Sure, which again is one of the reasons that we only looked at places with stable epidemics, rather than including ongoing outbreaks. Virtually all seroprevalence studies had some adjustment for test sensitivity and specificity

      1 reply 0 retweets 0 likes
    6. Health Nerd‏Verified account @GidMK 31 Aug 2020
      Replying to @GidMK @sangfroyd

      But I can't see the argument that there is a large element of bias in the small proportion of people who might become seronegative that are not already included in test sensitivity calculations

      1 reply 0 retweets 0 likes
    7. Josh Ketter‏ @sangfroyd 31 Aug 2020
      Replying to @GidMK

      Small if done within the 1-3 months that the sensitivity calc's were derived from. But it becomes quite large after that. The calculus changes, but you're treating it as fixed. If you accounted for this somehow, apologies. Wasn't obvioushttps://www.nature.com/articles/s41591-020-0965-6 …

      1 reply 0 retweets 0 likes
    8. Health Nerd‏Verified account @GidMK 31 Aug 2020
      Replying to @sangfroyd

      Ugh. What I've been trying to explain is that this is accounted for already in test sensitivity. It's part of the reason that you get false negatives (the main other being delay to seroconversion)!

      1 reply 0 retweets 0 likes
    9. Josh Ketter‏ @sangfroyd 31 Aug 2020
      Replying to @GidMK

      Are you developing your own test sensitivity calc for each study based on the dynamics of their epi timeline vs. dates samples were taken? Or are you taking the published sensitivities from the test manufacturer?

      1 reply 0 retweets 0 likes
    10. Josh Ketter‏ @sangfroyd 31 Aug 2020
      Replying to @sangfroyd @GidMK

      What I have been trying to explain is that if the test manu developed specs using PCR +ve vs. AB 1-3 months later, with a median follow-up of 2 months (wherein 90% of AB's still exist) Then a serology study is conducted in month 6 of an Epi (where 40% of AB's remain), it's under

      1 reply 0 retweets 0 likes
      Health Nerd‏Verified account @GidMK 31 Aug 2020
      Replying to @sangfroyd

      I mean, you can assume anything, but the evidence (incl the study you linked) mostly shows that antibody titres decrease then stabilise in most cases, and the majority of cases remain seropositive

      11:33 PM - 31 Aug 2020
      0 replies 0 retweets 0 likes

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