Time series COVID-19 circa 26 April 2020 by Dean Luis Dumlao, PhD

April 28, 2020
The first case of positive COVID-19 in the Philippines was detected on 30 January and the first death was reported on 1 February. The number of cases remain two for the rest of February. With both cases being non-Filipinos, it seemed that the Philippines will not be hit by what was still then an epidemic.
 
On 6 March, the cumulative number of cases doubled to four and then on 9 March more than quintupled to 23. When the World Health Organization (WHO) elevated the epidemic to a pandemic on 11 March, the cases in two days more than doubled to 48. By then, it was already obvious that the country will be hit hard. On 17 March, when the enhanced community quarantine (ECQ) became effective in the whole of Luzon, there were already 186 cases.

While the cumulative number of cases will only increase, the key to further understand the data is to look at the additional cases per day i.e. the first difference or the first integration in economics parlance. Still, the number of cases fluctuates daily. In finance and in time series, scientists and practitioners try to understand erratic series of numbers by smoothening the data using moving averages (MA). For example, stock market players often use MA to eliminate idiosyncratic changes and capture the long run trend or the secular movement of stock prices and indices. Known examples of applying the MA on COVID-19 include the New York Times 5-day MA and John King of CNN’s 7-day MA. Suppose we use halfway of the one to fourteen days of incubation COVID-19 in accordance to WHO which conveniently translates to a 7-day MA or 1-week MA.
 
The number of incidences and admittances to the hospital began to increase at an increasing rate on March 20. On 3 April, the incidences and admittances per day peaked at 316 and 171, respectively. On 5 April, the incidences and admittances per day declined to 261 and 143, respectively, on 6 April increased to 302 and 162, and then decreased for four consecutive days. On 7 April, it has become statistically official that we have passed the apex of incidences and admittances per day. 7 April was also the date that the number of recoveries then at five per day started to pick up. It was also the date that President Duterte decided to extend the ECQ to 30 April.


A key scientific question was whether the incidences and admittances per day would move in cycles or permanently decline. It turned out that these will cyclically decline. These numbers will continue to decline and reach what mathematicians call the local minimum on 10 April with 168 and 91 incidences and admittances per day, respectively. On 13 April, for the first time, the number of recoveries per day at 24 topped the number of deaths per day at 22. On the same day, the incidences and admittances per day became statistically officially on the upswing again; this is mere proof that the decision to extend the ECQ about a week before was right.

On 15 April, the 7-day MA number of deaths per day peaked at 24. On 17 April, the incidences and admittances per day reached its new peak or what mathematicians call the local maximum with 241 and 126, respectively. On 19 April, the incidences and admittances per day would be statistically officially on a downswing and the number of recoveries per pay which stood at 54 peaked. 
 
On 22 April, it became statistically official that recoveries per day mysteriously goes on down swing. If people were getting infected by the hundreds the past twenty to thirty days, they should sooner or later either recover or die. But given that the deaths per day tops at 24, either infected people remain sick for extended periods of time, number of recoveries have not been correctly reported, or that recoveries will cyclically increase.
 
 On 24 April, President Duterte decided to extend the ECQ further to 15 May. On that day, for the first time, the recoveries per day at 42 is greater than the admittances per day at 39. If trends remain which is still uncertain, it will mark the peak when hospitals are most distressed. After that, the net number of patients in hospitals will start to decline. It will be the day our medical front liners’ work will start to “ease” for lack of better term. 
 
The number of active COVID-19 positives will peak and decline from then on when the sum of the number of new deaths and new recoveries become greater than the number of new incidences. It should be an inevitable event. As the number of new deaths decline, the condition in which the number of COVID-19 positives will decline is for the number of new recoveries to go up. But as the number of new recoveries has mysteriously gone down, there is still no credible way to predict when the number of active COVID-19 will start to decline. 
 
Finally, the healing process of the nation will begin when the number of new recoveries become greater than the number of new incidences which should also be an inevitable event. That will happen when the number of new incidences declines which is cyclically declining, and the number of new recoveries goes up but as stated has mysteriously gone down. Until such time that the number of new recoveries go up statistically and conclusively, one cannot predict when the process of healing will begin.

 
 
Note: Positions taken are author’s and is not necessarily that of the John Gokongwei School of Management, Ateneo de Manila University.