An instructor conducted an experiment to determine the effects of two different methods of study on the amount students learned in introductory physics. The results showed that the average amount learned by the group using one method was greater than the average amount learned by the group using the other. However, the difference was not statistically significant. Which of the following is the most appropriate conclusion to be drawn?

The group of students attaining the higher mean score had studied more than the other group.

The better study method will have different effects for students of varying levels of ability.

There is a positive correlation between the results of the two methods.

There is a possibility that the difference between the two groups occurred by chance.