18 September 2006

Tricky Dengue Statistics

Here's a dengue morbidity and mortality update from the Philippines' DoH published in the local dailies last weekend:

Tricky statistical numbers, if you ask me. It paints an illusionary picture of decrease in the number of dengue cases and deaths. If you compare the 2006 column with the figures from my dengue post last year, you will note a very slight difference in the number of cases.

As of September 9 this year, and based on their advert above, the DoH says the Philippines has a total of 14,915 dengue cases. As of August 11 last year, however, we had a total of 14,142 dengue cases.

The DoH wants the impulsive observer to conclude that the overall dengue picture is actually good --- believe it or not --- as there are only 3 regions showing an increase in the number of cases over the same period last year.

But the comparison is erroneous. The 2005 figures above are the total number of dengue cases for that year.

Referring to the DoH table above, these 3 regions are the National Capital Region (where Metro Manila is) at 43.8 percent, Region IV-A (Calabarzon area) at 45.7 percent, and the biggest increase in the CAR area at 58.2 percent. Baguio City alone in CAR, accounts for more than 600 dengue cases. The rest of the regions show a decrease in the number of cases.

Mortality-wise, the DoH would like the careless observer to believe that there is really a more than 45 percent decrease in the number of deaths due to dengue.
Do not put your faith in what statistics say until you have carefully considered what they do not say. ~ William W. Watt
What the DoH advert forgets to mention is that the 2005 figures are the total number of dengue cases and deaths for that year, while the 2006 column only supplies figures up to September 9, 2006. These two are not comparable. It's amazing why they should even be compared. Partial figures and total figures are so different from each other. Any seasoned biostatistician will tell you that in this case, it's a mortal sin to compare partial figures with total figures. Unless, of course, you want to arrive at a wrong conclusion. Now, why would anyone want that?

The REAL dengue picture in the Philippines? By the looks of it, we are having the same trend as last year. Looking at the trend of dengue cases, we might end 2006 with more than 20,000 dengue cases again. A news report based on the DoH advert above has also drawn the wrong conclusions about the current dengue picture in the country.

What also alarmed me is this part of that news report:
At a Malaca├▒ang briefing, Health Secretary Francisco Duque said there was a 42 percent decrease in dengue cases and an 84 percent decrease in meningococcemia cases, compared to the same period last year.

[SOURCE: INQ7.net, 18 Sept 2006 ]

Oh, no! Even the DOH Secretary is feeding the wrong statistics and conclusions to the head of government. What will happen now?

Complacency or making people believe the wrong data will not kill the dengue virus. On the other hand, killing mosquitoes will. The least the DOH can do to help alleviate a cyclical arthropod-borne disease is be honest with its figures. If we do not know the extent of the problem, we may never be able to solve it.

I pray this is merely an honest mistake on their part, and nothing intentional.

10 reactions:

Sidney said...

98% of all statistics are made up. -Author Unknown-

Dr. Emer said...

Let us hope this is not the case here, Sidney. That would be too cruel a joke.

Tani said...

statistics are so confusing! you try to interpret them not realizing (if you're not a keen observer) that they are not true at all. anyway, dengue is alarming especially to lay persons. actually, i myself am bothered with the open canal behind our condo bldg... talk about dengue scare!

ipanema said...

hi doc, i can't seem to find the table (with the post) that you link to DOH. All I have are data from 1999-2002.

I've read the news article and the writer wrote referred to January - September 9, 2006 to the same period last year (2005):

2nd paragraph>>Based on DoH computations, there was an 86 percent increase in meningococcemia’s case fatality rate (percentage of people who died from the disease) from January to September this year
compared to the same period in 2005.

3rd paragraph-->>...there was a 42 percent decrease in dengue cases and an 84 percent decrease in meningococcemia cases, compared to the same period last year.

4th paragraph-->> From January 1 to September 9, there were 14,915 dengue cases but 188 patients succumbed to the mosquito-borne disease. There were 25,680 cases and 316 deaths during the same period last year.

6th paragraph-->> From January till September, there were 69 meningococcemia cases and 27 people died from the disease. There were 421 cases and 89 deaths in the same period last year.

I think with the above statements, the writer is referring to the period:

January - September 9 2005 AND
January - September 9 2006, hence her reference to...compared to the same period last year.

If this is the case, then there is a decrease. Therefore, DOH Secretary's statement is correct and the article is correct.

Know what I think is wrong? Some information from the table. It should have been written :
2006 (as at Sept.9) and 2005 (as at Sept. 9). This could be written below the years. Or they could write it below the table as annotation.

The first time I looked at the table I know there's something wrong. 2006 is not yet over, so there must be some point of reference. If one will write 2005, of course, we refer that as 1 whole year. And if 2006 is written, we mean the whole year too BUT check, it's only Sept. So, this I think is missing from the table.

Sorry for the long post. :)

tin-tin said...

doc, serious question.. is there a cure for dengue already?

bayi said...

Either it was a deliberate attempt to downplay the statistics or it was pure ignorance.

Either way, I would want to dramatize the danger so that people would take immediate action to reduce the instances of dengue. People's lives are at stake and this is no time to lull the people into complacency in the face of grave danger.

Moof said...

Dr. Emer, are the statistics derived from a national Administrative Database, or something else?

Is there a way to derive the accurate, complete numbers?

Dr. Emer said...

TANI: Health statistics may be confusing but it is necessary to understand them to get an accurate epidemiologic picture of any disease. But I agree with you. If the premise is wrong, the conclusion is wrong. And oh, better find a way to seal that open canal.

IPANEMA: Oh, Ipanema! I'm so sorry for making you belabor my point. No need to apologize for your long post. I think that pestiferous phrase "same period in 2005" IS the culprit in the DoH faux pas. Read this (you can also look at my 2005 dengue figures from my post last year), take note WHAT DATE that news was written, do some simple math, and you will know that the 2006 column in that DoH Table of Dengue Cases and Deaths DO NOT stand for the "same period in time" in 2005. What I cannot understand is WHY the DoH allowed this to be published under a banner title of "42 percent decrease in dengue cases." An erroneous table of numbers should NOT make that conclusion.

And please do not bother checking the DoH website for the same figures. It is not there. That's how sophisticated our DoH is. I placed the DoH link so you will know I'm not kidding when I say that its an empty site. Even its NEC division (website is here), which is supposed to handle facts about any disease outbreak, is devoid of current data about dengue. To think that this is the time of the year when dengue strikes. Who knows why? Maybe they do not think it is that important.

TIN-TIN: None yet. The best cure is still natural immunity. Vaccine development are still in Phase 2 trials. I'll try to discuss this in a future post, if and when my time permits.

BAYI: Do you still think they really care? Like you, I do hope it was merely an honest mistake.

ipanema said...

hahahaha...same old same old GOVERNMENT! What do they want to achieve in publishing that? I think there's even no counter check from the DOH Secretary's Office after the article was published. Otherwise, there should have been an erratum.

Dr. Emer said...

MOOF: You do not know the lengths one has to go through in order to get the correct numbers. Exhausting! Yes, I know. It's easier there in the US. Not here. It's older than old school here. *LOL* But my search has somewhat paid off. Read my latest post.