Don’t be Fooled by the Numbers in Drug Ads: How You Get to the Absolute Truth
A while back we posted, Don’t be Fooled by Pay-to-Play Online Doctor Referral Sites, about how it’s common for doctors to pay io be listed in online doctor referral services. (Doctors can pay extra to be listed first in your database search results.)
How Some Drug Ads Mislead
This time we caution you about how some drug ads mislead you.
Here’s an example of an actual news report headline, “New Wonder Drug Reduces Heart Attack Risk by 50%.” Sounds like a great drug, doesn’t it?
Yet it sounds significantly less great when you realize we’re actually talking about a 2% risk dropping to a 1% risk. The risk halved, but in a far less impressive fashion.
A factual headline would be, “New Wonder Drug Reduces Heart Attacks from 2 per 100 to 1 per 100.” Doesn’t sound like such a great drug now, does it?
The online watchdog group HealthNewsReview.org reports, that’s why using “absolute numbers” versus percentages matter. “Absolute numbers” provide you with enough information to determine the true size of the benefit.
The Tale of a 50% Off Coupon
Professors Steve Woloshin and Lisa Schwartz of the Dartmouth Institute for Health Policy & Clinical Practice explain absolute numbers versus percentage (relative numbers) in a creative way.
“… [it’s] like having a 50% off coupon for a selected item at a department store. But you don’t know if the coupon applies to a diamond necklace or to a pack of chewing gum.
Only by knowing what the coupon’s true value is—the absolute data—does the 50% have any meaning.”
So, 50% off a diamond necklace might be a savings of $5,000. While 50% off a pack of gum might be 50 cents. Absolute numbers tell the whole story.
The Bottom Line: Be Skeptical, Ask Questions
As a healthcare consumer, it’s wise for you to be skeptical anytime you hear a benefit size expressed as a percentage, for example, a 50% improvement or 50% fewer side effects.
You should ask yourself 50% of how many? Of 10,000 patients? Or 10 patients? Which result is significant and which is just blowing smoke?
Numbers matter. That’s how you get to the absolute truth.
Additional Reading
See also How to See Through the Hype in Medical News, Ads, and Public Service Announcements, my review of the book “Know Your Chances―Understanding Health Statistics”.
The Math Behind a 50% Reduction
“New Wonder Drug Reduces Heart Attack Risk by Half.” How was this claim calculated?
The Raw Data: In the research study, the 5-year risk for heart attack for:
-a group of patients treated conventionally was 2 in 100 (2%) and
-a group of patients treated with the new drug was 1 in 100 (1%).Absolute Difference: The absolute difference is derived by simply subtracting the two risks: 2% – 1% = 1%. Expressed as an absolute difference, the new drug reduces the 5-year risk for heart attack by 1 percentage point (or 1 in 100).
Relative Difference: The relative difference is the ratio of the two risks. Given the data above, the relative difference is: 1% ÷ 2% = 50%. Expressed as a relative difference, the new drug reduces the risk for heart attack by half, or 50%.
Absolute Numbers Versus Percentages:
How the numbers work (or mislead the reader)