Statistics - What are internal validity and external validity, and why

2. You read in a health magazine about a study in which a new therapy technique for
depression was examined. A group of depressed individuals volunteered to participate in
the study, which lasted about 9 months. There were 50 subjects at the beginning of the
study and 29 at the end of the 9 months. The researchers claimed that of those who
completed the program, 85% improved. What possible confounds can you identify in this
study?
4. What are internal validity and external validity, and why are they so important to
researchers?
6. What are the similarities and differences between within-subjects and matchedsubjects designs?
What is the purpose of conducting an experiment? How does an experimental design
accomplish its purpose?
What are the advantages and disadvantages of an experimental design in an educational
study?
What is more important in an experimental study, designing the study in order to make
strong internal validity claims or strong external validity claims? Why?
In an experiment, what is a control? What is the purpose of a control group? Of single or
multiple comparison groups?
What are confounds? Give an example of a design that has three confounds. Describe
three ways to alter the design to address these confounds and explain the advantages and
disadvantages of each.
What does “cause” mean and why is it an important concept in research? How are
correlation and causation related?
You are a researcher interested in addressing the question: does smiling cause mood to
rise (i.e., become more positive)? Sketch between-participants, within-participants, and
matched-participants designs that address this question and discuss the advantages and
disadvantages of each to yielding data that help you answer the question. Describe and

discuss each design in 4-5 sentences.