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Numbers about risks are risking our health

Adrienne Chan
Written By
Adrienne Chan
Numbers about risks are risking our health
Artwork by Louise Pau and Simon Tyler

Swap a burger for some nuts to halve the risk of heart disease

Drinking just two cups of milk a day 'can increase the risk of breast cancer in women by up to 80%'

Headlines like these permeate our everyday lives. And suddenly, we find ourselves sitting in our bedroom, not knowing what to get for breakfast anymore. But this is what news headlines are supposed to do. They should grab our attention and alert us of relevant information that might be useful to our decision making. It is up to us to educate ourselves on the spotlighted issue and contextualise the information provided.

Before diving into the chaos of health statistics that surrounds us, we first need to understand, what on earth is risk? In simple terms, risk represents the chance of something happening. For instance, the chance or the ‘risk’ of drawing a spade from a deck of cards is 1 in 4 or 25%. Does that mean if you draw four cards out of the deck at random, one of them will be a spade? If that’s the case then we would all be a poker champion. The number only tells us what is ‘expected’ to happen if we were to keep drawing the cards with a replacement for an infinite number of times.

Now that we understand the uncertain nature of risks, we are going to look at some common forms of risk representation in our everyday lives. In their paper tackling collective statistical illiteracy, Gigerenzer highlighted the effects of various ways to frame information on perceived treatment efficacy. In a phone survey study, participants were presented with three different screening tests for unspecified cancers.

  • Relative risk reduction: If you have this test every 2 years, it will reduce your chance of dying from this cancer by around one third over the next 10 years
  • Absolute risk reduction: If you have this test every 2 years, it will reduce your chance of dying from this cancer from around 3 in 1,000 to around 2 in 1,000 over the next 10 years
  • Number needed to treat: If around 1,000 people have this test every 2 years, 1 person will be saved from dying from this cancer every 10 years

The acceptance rate of the screening test was the highest when its benefits were presented in relative risk reduction.

This is likely due to the fact that relative risk reduction seems larger and causes intervention to be viewed as having greater benefits.

However, it is important to note that the three statements above are referring to identical benefits. And sometimes, or in fact, a lot of the times, improper phrasing of scientific findings could mislead the readers.

The take-home message here is to always trace back to the source of the information and locate the absolute risk. Only then, can we as an individual decide if a <0.0001% risk reduction is a worthy investment when pitted against opportunity costs or other risks such as potential side effects of treatment, costs of adopting a new supplement plan, emotional risks, and more.