樵客
講述親身經曆，感悟天地人生
給你一雙慧眼，明白疫情本相。
（所有中文為本人注解，看中文即知脈落，讀英文知算法細節和出處。如有異議，以英文原文為準）
死亡率，是衡量疫情嚴重程度的最重要指標。也是從平民到決策層都最為關注的。
標準的算法是，在疫情結束時（沒有在治療中的患者），死者占總確診病例的百分比。
但是，疫情在進展，人們更關注在目前的死亡情況，即時死亡比例（ current CFR），以調整適當的治療方法及社會對應決策（政治、經濟、民生等）。
可是，在疫情中（進行時），由於診斷標準和檢測方法及人為幹擾（如不檢測方針，以減少明麵總數維穩；或有意擴大病例數以降低死亡率），還有沒能及時匯總等因素，在某一特定時刻的確診人數並不確定。在使用標準算時，產生相當大的假象。
因此有必要引用專業人士的算法，而不是官方為粉飾太平而使用的算法（死亡數/累計確診數）。
下文取自：https://www.worldometers.info/coronavirus/coronavirus-death-rate/
How to calculate the mortality rate during an outbreak
The case fatality rate (CFR) represents the proportion of cases who eventually die from a disease.
Once an epidemic has ended, it is calculated with the formula: deaths / cases.
But while an epidemic is still ongoing, as it is the case with the current novel coronavirus outbreak, this formula is, at the very least, "naïve" and can be "misleading if, at the time of analysis, the outcome is unknown for a non negligible proportion of patients." [8]
In other words, current deaths belong to a total case figure of the past, not to the current case figure in which the outcome (recovery or death) of a proportion (the most recent cases) hasn't yet been determined.
The correct formula, therefore, would appear to be:
第一種規範算法：按病程計算即時死亡率（俺在以前的貼子中提到過）
如果知道然病程（從確診到死亡的平均天數），那麽在算“當下”死亡率時，要用死亡者確診時的總病患案例做為基數，而不是用死亡時的總病例數。
CFR = deaths at day.x / cases at day.x-{T}
(where T = average time period from case confirmation to death)
This would constitute a fair attempt to use values for cases and deaths belonging to the same group of patients.
One issue can be that of determining whether there is enough data to estimate T with any precision, but it is certainly not T = 0 (what is implicitly used when applying the formula current deaths / current cases to determine CFR during an ongoing outbreak).
Let's take, for example, the data at the end of February 8, 2020: 813 deaths (cumulative total) and 37,552 cases (cumulative total) worldwide.
If we use the formula (deaths / cases) we get:
813 / 37,552 = 2.2% CFR (flawed formula).
With a conservative estimate of T = 7 days as the average period from case confirmation to death, we would correct the above formula by using February 1 cumulative cases, which were 14,381, in the denominator:
Feb. 8 deaths / Feb. 1 cases = 813 / 14,381 = 5.7% CFR (correct formula, and estimating T=7).
T could be estimated by simply looking at the value of (current total deaths + current total recovered) and pair it with a case total in the past that has the same value. For the above formula, the matching dates would be January 26/27, providing an estimate for T of 12 to 13 days. This method of estimating T uses the same logic of the following method, and therefore will yield the same result.
第二種算法比較簡單易行, 使用目前累計死亡數和累計治愈數來估算。（就是杜編所使用的算法）
An alternative method, which has the advantage of not having to estimate a variable, and that is mentioned in the American Journal of Epidemiology study cited previously as a simple method that nevertheless could work reasonably well if the hazards of death and recovery at any time t measured from admission to the hospital, conditional on an event occurring at time t, are proportional, would be to use the formula:
CFR = deaths / (deaths + recovered)
which, with the latest data available, would be equal to:
3,303 / (3,303 + 53,708) = 6% CFR (worldwide)
If we now exclude cases in mainland China, using current data on deaths and recovered cases, we get:
290 / (290 + 1,481) = 16.4% CFR (outside of mainland China)
The sample size above is limited, and the data could be inaccurate (for example, the number of recoveries in countries outside of China could be lagging in our collection of data from numerous sources, whereas the number of cases and deaths is more readily available and therefore generally more up to par).
There was a discrepancy in mortality rates (with a much higher mortality rate in China) which however is not being confirmed as the sample of cases outside of China is growing in size. On the contrary, it is now higher outside of China than within.
That initial discrepancy was generally explained with a higher case detection rate outside of China especially with respect to Wuhan, where priority had to be initially placed on severe and critical cases, given the ongoing emergency.
Unreported cases would have the effect of decreasing the denominator and inflating the CFR above its real value. For example, assuming 10,000 total unreported cases in Wuhan and adding them back to the formula, we would get a CFR of 4.9% (quite different from the CFR of 6% based strictly on confirmed cases).
