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Are psychological biases universal or local?

By Estela Baldi.

Most behavioral science concepts are written in English and based on WEIRD (Western, educated, industrialized, wealthy and democratic) populations. Indeed, an article that analyzed research from six journals in various areas of psychology from 2003 to 2007 found that 68% of the research had a sample in the United States, 14% in English-speaking countries (United Kingdom, Canada, Australia and New Zealand) and 13% in Europe. In the case of Latin America, for example, the samples with these populations represented 1% of the total. Thus, there is a large evidence gap on how psychological principles are manifested in Latin, Asian, or Middle Eastern populations. Thanks to the visibility of this problem of representation, different projects have gradually been carried out that go beyond the borders of the Global North.


For example, Joseph Heinrich, who coined the term WEIRD, conducted a study in the Machiguenga community, located in the Peruvian Amazon. His objective was to collect evidence on the differences in decision-making between different WEIRD populations and the Machiguenga. The experiment focused on observing economic decision making, based on a game called "Ultimátum". This dynamic consists of giving an amount of money to a participant, under the condition that in order for him to keep the amount, he must offer a percentage of this money to a partner and that the offer be accepted by him. Comparison of the Machiguenga results with existing data from WEIRD communities suggested that economic decision-making may be strongly influenced by cultural differences.

While players representing a WEIRD population considered that the best strategy to ensure that their partner would accept the money was to offer around 50%, members of the Peruvian ethnic group showed a different negotiation strategy.

On average, the Machiguenga made offers that involved the other participant receiving only 26% of the amount. The recipients of the offer, when evaluating their partner's negotiation, showed little expectation of receiving a balanced proportion, since they did not reject offers that meant that they would keep that percentage of the money and the other participant the rest. In other words, they preferred to accept the negotiation and take a smaller percentage than for both players to receive none of the money.

local bias, endowment effect, behavioral sciences
Image 1. Machiguenga, Amazon, Perú

There is also another study by Coren Apicella et al., that explored the concept of endowment effect in an ethnic group called "Hadza", located in northern Tanzania. The concept of endowment effect, introduced by Richard Thaler in 1980, explains the increase in the value of an asset for an individual when it becomes part of his or her membership. In the experiment with the Hadza community, participants were randomly given one of two different colored lighters that they used to light campfires, and then given the opportunity to exchange the lighter for one of a different color. The results of the study in the Hadza population reflect a different manifestation of the endowment effect bias than that observed in Western populations in similar experiments. In the case of the Hadza, they proceeded to exchange the lighter 50% of the time, suggesting that the endowment effect bias was not observed in their decision process.

local bias, endowment effect, behavioral sciences
Image 2. Hadza, Tanzania. Photo captured by Joanna Eede of Survival International.

From the two cases presented, it could be concluded that human behavior manifests itself differently depending on the context. In the aforementioned studies, it is shown that a person's way of deciding is also conditioned by his or her culture. In a very recent interview with Daniel Kahneman (Nobel Prize in Economics 2002), when asked about the differences in the manifestation of endowment effect in the case of the Hadza, he mentioned "I have no doubt that there is a possibility that certain cultures have a norm of exchange where the polite thing to do is to exchange and not to hold on to what one has".

We believe it is important to understand that when constructing a behavior change intervention, it should not be designed based on evidence that has only been tested in WEIRD communities. Rather, we recommend incorporating the contextual analysis of the population being studied. Human psychology is affected by its environment, so if you want to understand how a person's mind works, you need to study the individual, along with his or her political, economic, historical, social, and technological context. Thus, when designing solutions for Latino populations, it is necessary to take into account the cultural, systemic and structural aspects, which are factors that greatly influence the decision making process of these populations.


  1. If you wish to know more details about the Machiguenga (Matsigenka) people, we recommend you to consult the following link:

  2. If you would like to learn more about the Hadza, we recommend the following link: Hadza (


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