Panel studies involve a special type of reflexive control, which means that the target subjects who receive an intervention are compared to themselves by use of before and after measurements. Panel studies are a repeated-measures design and typically use survey methods for data collection, although interviews and other qualitative data collection methods may also be involved. Panel studies that embed qualitative samples inside a large-scale survey design can be conducted in ways that will yield valuable information to policy makers and administrators. These embedded subsamples may be representative of the whole survey universe or may be purposive and designed to understand one particular category.