The Off-by-100% Bias: Why numbers don't always tell the truth

Posted by Anders Toxboe on August 21, 2024 · 4 mins read

---

Have you ever seen a product advertised as being “150% more effective”? It sounds impressive, doesn’t it? But did you know that many people actually underestimate the magnitude of such a percentage increase? This phenomenon, known as the “Off-by-100% Bias,” can have significant implications for marketing and consumer behavior.

The Off-by-100% Bias refers to our tendency to underestimate the size of percentage changes that are greater than 100%. In simpler terms, when we see a product that’s claimed to be 150% better, our minds often don’t fully grasp the extent of that improvement. This can lead to missed opportunities for businesses and suboptimal decision-making for consumers.

Why Does This Happen?

There are a few reasons why we might fall victim to the Off-by-100% Bias:

• Anchoring. We often anchor our judgments on the initial value. So, if a product is initially priced at $100 and is then advertised as being 150% more effective, we might anchor on the $100 price and underestimate the actual increase in value.
• Cognitive Fluency. Large percentages can be more cognitively demanding to process. Our brains might take a shortcut and underestimate the magnitude of the change to simplify the information.
• Reference Points. Our understanding of percentages is often influenced by our personal experiences and reference points. If we’re not familiar with a particular product or industry, we might have a harder time accurately assessing percentage claims.

The Off-by-100% Bias can have a significant impact on consumer behavior. When we underestimate the magnitude of percentage increases, we might be less likely to perceive a product as being a worthwhile investment. This can lead to missed sales opportunities for businesses and suboptimal choices for consumers.

A Case Study: The Off-by-100% Bias Experiment

To better understand the Off-by-100% Bias, researchers conducted a series of experiments. In one experiment, participants were asked to estimate the size of different percentage increases. They were presented with scenarios such as “A product is 150% more effective” or “A price has increased by 200%.”

The results were surprising: Participants consistently underestimated the magnitude of percentage increases greater than 100%. For example, they often perceived a 150% increase as being closer to 50% or 75%.

Experiment Details:

• Study: Fisher, M., & Mormann, M. (2023). The Off by 100% Bias: The Effects of Percentage Changes Greater than 100% on Magnitude Judgments and Consumer Choice. Journal of Consumer Research, 50(3), 367–381.
• Participants: A group of individuals from various backgrounds.
• Procedure: Participants were presented with different scenarios involving percentage increases and asked to estimate the magnitude of the change.
• Findings: Participants consistently underestimated the size of percentage increases greater than 100%.

Designing with the Off by 100% Bias

Understanding the Off-by-100% Bias can help designers and marketers improve their communication strategies. Here are a few tips:

• Use clear and concise language: Avoid using overly complex language or jargon that might confuse consumers.
• Provide context: Give consumers a reference point to help them better understand the magnitude of percentage increases. For example, you could say “Our product is 150% more effective than the leading competitor.”
• Use visual aids: Graphs, charts, or other visual aids can help consumers visualize the magnitude of percentage changes.