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Plesse igmore amd axxept applogies in adbance fir anu typos
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tdgeek:
DS248: Incidentally I will post a plot in the data thread a bit later showing that the 'drop' in cases to 8 yesterday is an illusion. In reality our new local cases confirmed per day has remained ~flat over the last four days (at ~12/day). In fact at 13, yesterday was the largest number over the last four days. ...
Can you explain. I see the 8 cases advised today. Great. All are related to existing cases. ...
Your comment?
Consider five significant dates: Date infected; Date of symptom onset (if any, but normally 5-6 days after infection); Date tested - date on which sample is taken from a person by a District Health Board community testing centre or medical practice etc (test organisation). Sample then sent to a lab for testing; Date of report - date that the test lab reports the result, which generally seems to be 1 - 2 days after the date tested (though anecdotally sometimes can be longer); Press release date - the date on which that result is included in the MOH daily briefing. Could add date of infectiousness to that but not needed in this explanation.
The trend of new cases vs date infected would be best for assessing prevalence of COVID-19 vs time but that is often unknown so is not possible. The next best option would be to plot new cases vs onset of symptoms. Hong Kong does provide that info (for those symptomatic at time of testing) and Taiwan does for some cases but I am not aware of other countries that do so, at least publicly. Probably there are but certainly not NZ. From the MOH publicly released individual case data, the best we can do is look at the trend of new cases vs 'date of report' which I assume to be effectively date of confirmation that a person is COVID-19 positive. It would be helpful, with zero privacy issues and very little effort if MOH at least included 'date tested'. But 'date of report' at least is a reasonable proxy for that since in most cases the results (if positive) seem to be available within a day or two of testing.
'Press release date' is a poor substitute for 'date tested'/'date of report', at least for the MOH data here in NZ as it is very sensitive to when results come into MOH and when they tally them. In the MOH briefing the 'new' cases reported (but called 'change in last 24 hours on their website', which seems more accurate) typically include cases reported over the day or two before the briefing (usually most the day before), and sometimes a few from earlier dates. And recently often one or two reported earlier in the day of the briefing.
Unusually, the data provided in the MOH briefing on 16 Apr, included 7 cases (1 imported, 6 other) that had a 'date of report' of 16 Apr; that is cases that had been confirmed earlier in the day of the briefing.
The press briefing yesterday (17th) added a further 8 (1 imported, 7 other) to the total with a 'date of report' of 16 Apr. There were also a few +1 & -1 for other dates but they cancelled out. And there were none for the current day (17th), hence the headline 8 'new' cases at the press briefing. Net just 8 added to the 16 Apr report date. Which on the face of it made our trend look very good, heading steeply down to near zero. But as I noted the headline 8 new cases yesterday is an illusion - they constitute only ~half the cases reported by test labs on 16 April (reflecting samples taken ~2 days earlier).
As per the plot below, the number of new cases vs 'Date of report' has been reasonably flat for the last four days. In fact an uptick in new cases on the 16th (no data yet for the 17th). Definitely not a sharp downwards trend as the headline press release data suggested. NB: plot below is similar to the one I previously posted but I have included total new cases as well as local (imported being the gap between the two curves).
It will be interesting to see today's figures. In this instance, no cases for 17 Apr have been publicly released yet so today's figure will be 'ground up'. But also need to be aware that tomorrow's press release may include some for the 17th so the figure for the 17th in the individual case data they release today may not be complete (equally the figure for the 16th may still be subject to change).
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My views (except when I am looking out their windows) are not those of my employer.
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My thoughts are no longer my own and is probably representative of our media-controlled government
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