Pennebaker and Francis (1996) used an experimental design to test their hypothesis that students who write about their emotional experiences associated with adjusting to college would have better health and academic outcomes than students who don't write about their experiences.

The independent variable was type of writing. Pennebaker and Francis used two conditions. The "treatment condition" was emotional writing, and the "control condition" was superficial writing.- Click on the boxes for "Emotional Writing Condition" and "Superficial Writing Condition" to see what students' experiences were like in this study.

Emotional Writing Condition

Superficial Writing Condition

To assess the effect of the independent variable, Pennebaker and Francis measured several dependent variables: health outcome, academic outcome, and cognitive change. Thus, they recorded how many times each student in the experiment visited the health center for illness during the academic year, student's GPA after the fall and spring semesters, and their language use over the 3 days of writing (i.e., number of insight and causal words). Look at what you wrote in one of the conditions. How many insight words did you use (e.g., realize, see, understand)? How many causal words did you use (e.g., because, why, reason, thus)? Pennebaker and Francis measured how many of these words students used over the 3 days of writing.

Pennebaker and Francis hoped to infer that emotional writing causes students to be healthier and academically more successful than superficial writing, and that these beneficial outcomes were related to cognitive changes. But to do so, they had to rule out possible alternative explanations.

One alternative explanation concerns the fact that different students participated in each condition. The two groups of students may have differed naturally in their health and academic ability and their tendency to search for meaning in the events that happen to them (among other things). However, we can rule out these alternative explanations for any differences in outcomes because Pennebaker and Francis randomly assigned participants to the conditions of the experiment. This makes the two groups of students equivalent, on average, before they did any writing.

Another alternative explanation concerns holding conditions constant. Is it possible that students' experiences in the two conditions differed in ways other than what they wrote? Any potential differences become alternative explanations for differences in outcome at the end of the study.

To hold conditions constant, Pennebaker and Francis had participants in both conditions write on the same days of the semester, for the same amount of time, in the same classroom. The experimenters conducting the study didn't know which condition students were in, so there was no way students could be treated differently.

Because Pennebaker and Francis conducted a controlled experiment, we can infer that emotional writing, compared to superficial writing, caused the different outcomes in their experiment. Their experiment had internal validity.