But they’re all good dogs

Q: Did you see dogs are better than lateral flow tests for detecting Covid?

A: No

Q: The Guardian says: Dogs can better detect Covid in humans than lateral flow tests, finds study. With 97% accuracy!!

A: That’s the detection rate in people with Covid. The detection rate of Covid in people without Covid is 9%, which is a lot higher than you’d like.

Q: Where did they find the people?

A: It was people turning up to a testing centre in Paris, though since 109 out of 335 had Covid, it can’t really have been representative. The test positivity rate in France as a whole is only 4.5% at the moment and peaked at 15.9%

Q: Is 335 people enough?

A: Potentially, though the study initially planned to get 2000 people

Q: The story says lateral flow tests correctly identify on average 72% of people infected with the virus who have symptoms, and 58% who do not. That sounds really bad. Why does anyone use them?

A:  There’s a lot of variability between tests: some of them are better.  Also, they have much, much lower false positive rates than the dogs — around half a percent.  Since there’s a tradeoff between conservative (giving false negatives) and being sensitive (giving false positives), you can’t just compare the sensitivity of two tests that have a ten-fold difference in false positive rate.

Q: Still dogs would be quicker, and you could just use the real test in people the dogs picked out

A: That has potential, but dogs don’t scale all that well. You need to train and test each dog; they can’t just be mass-produced, boxed up, and mailed around the country.  And dogs aren’t that much quicker — this isn’t walk-past sniffing like the beagles looking for smuggled food at Auckland airport; you need to stick a pad in your armpit for a couple of minutes.

Q: How much of the spin is from the research paper and how much is coming from the newspaper.

A: The researchers are reported in the French source: “Ces résultats confirment scientifiquement la capacité des chiens à détecter une signature olfactive de la Covid-19“, souligne l’AP-HP, précisant que cette étude, pas encore publiée dans une revue médicale, est “la première de ce type réalisée au niveau international“.

Q: J’ai pas de clue que that means

A:  “These results scientifically confirm the ability of dogs to detect an olfactory signature of Covid-19 “, emphasise [the hospital], specifying that this study, not yet published in a medical journal, is ” the first of this type carried out in international level “.

Q: So it’s not just the Guardian

A: No.