Describe the following hypothesis and see whether you would use an experimental or observational design. Explain why you chose either type of design. Which statistical test should you choose for this situation?

Study:

A researcher would like to determine whether or not a new type of therapy improved the children's speech.

A random sample of 31 children with a speech defect were enrolled in a new type of therapy. Improvement was measured by how many words the children could correctly pronounce from a standardized word list. The researcher would like to evaluate this hypothesis in a short time period, such as one month.