Final answer:
The chat format is the independent variable, and the strength of the relationship is the dependent variable in this study.
Step-by-step explanation:
In the research scenario described, the chat format is the independent variable because it is the factor that is being manipulated by the researchers to examine its effect on the strength of relationships, which is the outcome of interest. The strength of the relationship, which is reported by the couples as being stronger for those who video chat compared to those who rely on text, is the dependent variable. This is because the dependent variable is what is being measured by the researchers to see how it is affected by changes in the independent variable. In experiments, it is common to manipulate the independent variable to determine if it has a causal effect on the dependent variable.