Interesting psychology experiments 1: The marshmallow experiment


In the late 1960s, Professor Walter Mischel from the Stanford University started a set of studies investigating delayed gratification in young children. [1]  In the original studies, the procedure was the following: Children, between 3 and 5 years old, were given a marshmallow and were told that they would get a second marshmallow if they wait long enough and don’t eat the first one. The time until the child started eating the marshmallow was measured, the upper limit being 15 minutes because then the experimenter came back with the promised second marshmallow.

Interestingly, follow-up studies showed that the duration of time the children waited for the second marshmallow correlated with the achievements of them many years later. Children who waited longer than others in this experiment tended to  have more success in school, higher SAT scores, lower BMI (Body Mass Index), higher income and more successful marriages later in life.[2]

The common interpretation of these findings was that self-discipline is the factor causing the different times children are waiting during the experiment. The idea behind this is that high self-discipline carries on into later life and enables the children to have a more successful life.

This interpretation was questioned by a recent study with a relatively low sample size. This study wanted to investigate whether rational decision making in the form of the assessment of the reliability of the environment is also an important factor. Previous studies indicated that uncertainty about the arrival of the second marshmallow decreases waiting time. This study specifically intended to test the difference in waiting times for two different conditions: The reliable and the unreliable condition. Their hypothesis was that children in the reliable condition will view the situation as more reliable and therefore wait longer, the opposite being expected for children in the unreliable condition.

The researchers changed the protocol to include the reliable and unreliable conditions in their experiment: Before starting the actual marshmallow task, they completed two different aspects of the experiment. First, the experimenter brought a very limited set of crayons and a piece of paper to the room where the child was sitting and said that he could bring additional crayons from the other room. The child naturally wanted more crayons and in the reliable condition they received those soon while in the unreliable condition the experimenter apologized and said that no additional crayons were in the other room. This was repeated with a sticker: In the reliable condition the experimenter brought a larger sticker from the other room while in the unreliable condition the child had to use a smaller sticker despite being promised a larger one. Afterwards the marshmallow task was completed in the way described above.

Their findings were statistically highly significant: The children in the reliable group waited for a mean time of 12 minutes and 2 seconds while the children in the unreliable group waited for a mean time of 3 minutes and 2 seconds. This supports their hypothesis that the child’s assessment of the reliability of the situation is a contributing factor to the duration of time waited.  This also has implications for the original findings: Depending on the background of the children their belief in the reliability of the world can differ, resulting in a different duration of time they wait. While this doesn’t imply that self-discipline isn’t also a contributing factor, it indicates that it’s not the only one.

To sum up, the marshmallow experiment is a surprisingly efficient predictor of the success of children later in life. Early interpretations of this included mainly self-discipline as the cause of both the longer waiting time and the later success in life while a recent study suggests that the explanation is a more complex one and has to include the ability to make rational decisions.

This blog post is part of the series “Interesting psychology experiments”.
See also:
Interesting psychology experiments 2: Car crash study
Interesting psychology experiments 3: Contagious yawning works with dogs

Photo source: wikimedia

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