I've added the number of test results reported per day, and the percent positive of those test results, to the table. (Also added today's figures.)
The columns are:
date
total confirmed cases to that date
increase factor of total confirmed cases for the day (rounded to two decimal places)
new confirmed cases for the day
number of test results for the day
percentage of test results positive
"S" indicates Saturdays and Sundays, which might affect the timing of reporting and thus shift the numbers of cases between days.
"*" and "+" indicate a new all-time high for new confirmed cases on that day.
Code:
3/21 525 1.27 112 S
3/22 646 1.23 121 S
3/23 777 1.20 131
3/24 1159 1.49 382 4827 8% + <--- business closures / lockdown
3/25 1838 1.59 679 6045 11% +
[COLOR="SeaGreen"]3/26 2417 1.32 579 3827 15%
3/27 3240 1.34 823 5750 14% +
3/28 4257 1.31 1017 5678 18% * S[/COLOR]
[COLOR="RoyalBlue"]3/29 4955 1.16 698 4017 17% S
3/30 5752 1.16 797 3727 21%
3/31 6620 1.15 868 4142 21%
4/01 7738 1.17 1118 4803 23% +
4/02 8966 1.16 1228 4870 25% +
4/03 10402 1.16 1436 6354 23% *[/COLOR]
4/04 11736 1.13 1334 5838 23% S
4/05 12500 1.07 764 3137 24% S
[COLOR="DarkRed"]4/06 13837 1.11 1337 4992 27%
4/07 15202 1.10 1365 4915 28%
4/08 16790 1.10 1588 6167 26% +
4/09 18941 1.13 2151 7447 29% *
4/10 20974 1.11 2033 7414 27%
4/11 22860 1.09 1886 6404 29% S
4/12 25475 1.11 2615 7954 33% * S[/COLOR]
[COLOR="SeaGreen"]4/13 26867 1.05 1392 5319 26% <--- 1.5 hr. change in data closeout time
4/14 28163 1.04 1296 4502 29%
4/15 29918 1.06 1755 5472 32%
4/16 32181 1.08 2263 8750 26%[/COLOR]
It's pretty clear that day to day differences in the timing of test result completion (or reporting) cause day to day variations in the numbers. For instance, it's pretty obvious that the anomalously low figure on 4/5 is the result of fewer test cycles completed that day. However, such delays can only shift "new" cases by a day or two. Longer-term trends such as the drop in rate from the "blue" period to the "red" period can't just be an artifact of such anomalies.
It also appears the figures from 4/14 and 4/15 were artificially low due to fewer (relative to prior days) test cycles being completed on those days, pushing those results forward to today's all time high number of test results and today's higher (but not all-time high) number of new cases. A similar weekday effect (with fewer results reported earlier in the week and more on Thursday and Friday) might have happened last week as well, but no such pattern extends to previous weeks.
On 3/24, the first date on which I could derive exact figures for new test results that day from the data available, testing in Massachusetts had just ramped up to an effective level, with over a dozen different labs reporting results, versus three labs two days earlier. (The 4,827 tests completed on the 24th were over 35% of the total number of MA tests completed, as of that date, since testing began.)
It's hard to pin down a reason for the low early percentage of positive tests, but the percentage itself speaks against there being a large backlog of symptomatic patients who hadn't yet been tested, thus artificially lowering the early case figures. The percent positive trended upward over time, but settled in the range of about one fourth to one third of all test results after the first week. More precautionary (as opposed to diagnostic) testing would tend to decrease the positive rate, while a dramatic proliferation of asymptomatic cases would tend to increase it. Different effects of that nature can't be separated out. But the lack of large (let alone sudden) changes in either of those stats in the past 3 weeks does not support any hypothesis that the apparent case rate is being artificially boosted by increased testing capturing a higher percentage of the actual cases, nor artificially suppressed by any drop-off in testing.
