This worksheet gives students 4 excercises in designing a case study. Each exercise presents a difference scenario and asks a series of questions about study design.
Use the Sample Size Calculator to determine the sample size you need in order to get results that reflect the target population as precisely as needed. You can also find the level of precision you have in an existing sample. The site also describes terms you need to know to understand confidence intervals and what they mean.
This resource defines and explains standard deviation and the normal distribution.