There was a blog post on HN yesterday from the Wikimedia Foundation. It was about the impact banners had on donators for the annual fundraiser.

Wikimedia Foundation has been showing a set of banners to the visitors of Wikipedia in order to point out that the annual fundraiser is running and motivate them to donate.

Two banners were the main focus of the post. They included a quote as well as the name of a donator, the date of the donation and the amount donated in USD.

The first one (#18) was about a USD 1.95 donation.

The second one (#22) talked about a USD 200 donation.

The post, using data about the average gift donated when motivated by a particular banner, concluded that banner #18 resulted in a average gift of USD 18.57 and banner #22 in an average gift of USD 31.80 (an increase of 71%!!)

Rand Montoya, Head of Community Giving, asked the readers to share their thoughts on the phenomenon.

The Anchoring and adjustment heuristic is my answer.

According to Wikipedia, “Anchoring and adjustment is a psychological heuristic that influences the way people intuitively assess probabilities. According to this heuristic, people start with an implicitly suggested reference point (the “anchor”) and make adjustments to it to reach their estimate. A person begins with a first approximation (anchor) and then makes adjustments to that number based on additional information.”

Tversky and Kahneman were the first to study this heuristic in the paper “Judgement under uncertainty: Heuristics and Biases” in 1974.

In one of their first studies, the two showed that when asked to guess the percentage of African nations which are members of the United Nations, people who were first asked “Was it more or less than 45%?” guessed lower values than those who had been asked if it was more or less than 65%. The pattern has held in other experiments for a wide variety of different subjects of estimation.

Moreover, in his book “Predictably Irrational: The Hidden Forces That Shape Our Decisions” (which I am currently reading), Dan Ariely conducts a similar experiment.
An audience is first asked to write the last 2 digits of their social security number, and, second, to submit mock bids on items such as wine and chocolate. The half of the audience with higher two-digit numbers would submit bids that were between 60 percent and 120 percent higher than those of the other half, far higher than a chance outcome.

Mr Montoya, to sum up, this is why you see the difference in average gifts donated by Wikipedia users.
Thank you for sharing the data with us and giving us the opportunity to observe another experiment of the anchoring heuristic in action.