7 Apr 2020

Data scientist says today could be turning point

From Nine To Noon, 9:09 am on 7 April 2020

A team of data scientists tracking the Covid-19 virus and advising the government, says today's new case update could signal a turning point. 

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Photo: Ministry of Health

Former Assistant Reserve Bank Governor and executive director of the economic think-tank, Motu, Dr John McDermott, is leading the data science team at the Asian macro-economic advisory firm, Wigram Capital Advisors. 

The group's projections of what would have happened if the country had not gone into lockdown were cited by the prime minister on Sunday. She said the modelling suggested the country might have had 4000 cases of Covid-19 were the country not in lockdown.

The number of cases as of yesterday is 1106 and yesterday saw a slight decrease in the number of new cases to 67, despite an increased number of tests being done.

The Director-General of Health Dr Ashley Bloomfield has cautiously welcomed what appears to be a levelling off of new cases in recent days despite a higher number of tests.

Dr McDermott said if today's new cases are under 60, it could be the start of the curve flattening.

He said Wigram Capital Advisors is a firm which is generally focused on what is happening economically in Asia, but it has invested heavily in a data science approach which can be used to watch data and then forecast developments.

"We're just taking the data and then putting it through standard algorithms and then having a look at what then happens."

The two vital pieces of information are the number of new cases and an assumption about how long it takes a primary case to pass on to a secondary case, Dr McDermott said.

"You can then monitor developments in real time, you can forecast what's going to happen in the next seven days or so and with that information, with that evidence, it can really anchor your decision-making about what you need to do."

He said it was a complex process and most of the frameworks and models assume a single outbreak and then take it from there.

But Dr McDermott said that was not the situation being faced at the moment.

"We're facing a situation where there's multiple outbreaks, the data's contaminated and you just have to do the best you can with the available information."

The reproduction rate of the disease shows from a given primary case how many people that primary case will infect on average.

It is important to monitor this because it indicates how transmissible the disease or virus is, he said.

"What you need to do is recalculate that every single day, monitor it, and if that number, the effective number starts to fall that's the first signal that your interventions are starting to make a difference."

He said he is cautiously optimistic that the lockdown is seeing some results in New Zealand.

He said a virus outbreak has three phases: the first is exponential growth, while New Zealand is currently in the second phase where this has slowed to linear growth, where the number of cases keeps increasing but is not out of control.

"The third phase is you need to see cases actually start falling and I suspect we're about a week behind Australia, they're seeing their cases fall.

"Given the nature of the virus and how long it takes, it can incubate and how long it takes to spread you and what we're seeing overseas, you really need to be about 12 to 14 days out from the lockdown to see if what you're doing really is making a big difference - but right now it's looking really promising."

He said the number of new Covid-19 cases in New Zealand have been roughly constant at up to 80 new cases a day, but if the country had been on an exponential growth curve, there would have been massive increase in the number of cases.

Dr McDermott said he is hopeful the number of new Covid-19 cases is about to start falling.

"The number I'm hoping for is that we see a fall in the number of new cases, so yesterday we had 67, if we start seeing a number in the 50s, we'll say yes we're on a downward trend and then the day after tomorrow if it's in the 40s, we can say we're on the path to eliminating cases."

See all RNZ coverage of Covid-19.