This article is a supplement to Philstar.com NewsLab's special report on Duterte's war on drugs.

MANILA, Philippines — President Rodrigo Duterte's claim that there are 4 million addicts in the Philippines is "within the realm of possibility," the Dangerous Drugs Board says. The math, however, does not support this assertion.

According to the DDB's 2015 Nationwide Survey on the Nature and Extent of Drug Abuse in the Philippines released in September 2016, there are around 1.8 million drug users in the Philippines, around 2.3 percent of the population.

This is the official figure, although the president has repeatedly mentioned 4 million users, whom he has characterized as addicts and as "slaves."

Philippine Drug Enforcement Agency Director General Isidro Lapeña, meanwhile, has been quoted in GMA News' "Balita Pilipinas" as saying there are 3 million addicts in the Philippines. He cited the same DDB survey.

"Pero may margin of error kasi iyan na plus or minus five percent, so it can even go as high as—so 2.3 plus 5 percent, that's 7.3 percent. That's even higher than the global average," DDB Chairman Benjamin Reyes told Philstar.com in an interview this month. The United Nations Office on Drugs and Crime estimates a global average of 5.2 percent.

"So, 'yung sinasabi ni president na four million? It's actually probable. Kasi nga, pasok siya doon sa margin of error eh," he said.

This was a reiteration of the DDB's position, sent in December 2016 by Corazon Mamigo of the board's Policy Studies, Research and Statistics Division, that "the claim of President Duterte that there are an estimated 4 million drug users in the Philippines is within the realm of possibility." She said, citing the same margin of error, that there may be as many as 5.7 million drug users in the country.

But the margin of error in the 2015 Nationwide Survey on the Nature and Extent of Drug Abuse in the Philippines is ±0.9 percent according to the DDB's presentation when the survey results were released last year and in the full report that was released to Philstar.com.

Asked to explain what the basis was for assuming the margin of error of ±5 percent, Reyes pointed to the 95 percent confidence level. "[That] means you have ±5 percent chance of not being correct," he said.

Doing the math

But Alyson Yap, a full-time member of the faculty at Ateneo de Manila University's Department of Quantitative Methods and Information Technology, disagrees with the assessment and called the conclusion dangerous.

Members of ADMU's Department of Quantitative Methods and Information Technology said the numbers don't add up.

Yap, who teaches combined statistics and operations management, said that using the the rate and confidence level used in the DDB report, the range would actually be "between 0.0185 to 0.0267 or between 1.85 percent to 2.67 percent only." That is around 1.4 million to 2 million people.

He said that the DDB may have gotten the +-5 percent error margin from the 95 percent confidence, an approach he disagreed with strongly in terms that cannot be published here.

"If we are to look at the upper bound of this proportion, from the estimated 1.75 million drug users, the maximum possible drug users is just roughly 300,000 (318,503.58 to be exact) more," he said.

Other data points to drug problem

Despite the discrepancy in estimates, DDB data indicates that the number of drug users was on the rise between 2010 and 2015.

In its December letter to Philstar.com, the DDB said that surveys "should be used with other data sources which can validate an observation."

The 2015 survey includes input from the Bureau of Jail Management and Penology, the Philippine National Police and the Philippine Drug Enforcement Agency and DDB said the increase in the number of arrests and inmates indicates a rise in the number of drug users.

The PNP, for example, made 44,453 drug-related arrests in 2015 against 5,002 in 2011. "Although this can be interpreted as an increase in efficiency of carrying out the task against dangerous drugs, improvement in efficiency alone cannot make such high increase in arrests if the population of dangerous drugs violators has not increased tremendously," the DDB said in its report.

DDB Chairman Reyes said that the nationwide surveys, which are done every three years, cannot be compared with each other because of changes in methodology in each one. He said that the differences can be attributed to budget constraints and the need to bid the project out to research firms.

He said, however, that the 2016 survey will likely be the baseline for future surveys.

Reyes said that it is better for programs to target the upper limit. "Sa perspective ng program management, you always target 'yung mas mataas. 'Di baleng mag-overshoot, [basta] huwag kang kulangin."

Not all users are addicts

Although the DDB is firm that there may actually be 4 million drug users in the Philippines, Reyes explains that not all of them are addicts or even drug dependents. He said that many—including the president—lump drug use and addiction together but that "technically and definitely, they are different."

"There's a big difference between drug use and drug dependence," he said, stressing that treatments for those cases differ. The DDB, which sets drug policy, has recommended four levels of treatment for dependence and addiction.

Those with severe substance use disorders—around one percent of users—are supposed to undergo six-month in-patient programs in rehabilitation centers. Between two to ten percent of users, those with less severe dependence on drugs, can be treated through out-patient programs.

The rest are for community-based treatments and interventions that the local anti-drug abuse councils will set up. The DDB and the Department of the Interior and Local Government are already working to set up and strengthen community-based programs, which, Reyes said, are the most important front in fighting the country's drug problem.

He said that if the local ADACs fail to give recovering addicts and dependents post-treatment support, there is a risk that they will return to using drugs. "Pag ganun ang nangyari, baka may mga magsasabi na hindi gumagana ang rehabilitation kaya huwag na lang," he said. — Philstar.com NewsLab; Videos by Efigenio Toledo IV; With reports by Kristian Javier