How many nurses should we observe and interview?

Some interested parties have questioned the number of nurses we will be interviewing and observing in each practice. For instance, nurses in a multi-nurse practice may feel “jilted” if one or more of their colleagues are observed and interviewed and they are not. The research team considered the options of observing more than two nurses at any one practice, and of observing two nurses while interviewing a different two. Ultimately we decided that we will conduct only two observations and two interviews with the same nurses in each practice, as originally planned. There are many reasons for this:
1) We wish to gain an overview of what practice nurses do, and by visiting 24 practices and observing up to 48 nurses, we believe this will be achieved. We do not need to know what every nurse in every practice is doing.
2) Our pilot and completed practice visits indicate that the roles of other nurses in the practice are often mentioned in the interviews.
3) We do not have the budget to complete anymore observations and interviews than those scheduled.
4) We wish to minimize the time we spend in any one practice.
5) Rapport develops between the researcher and the nurse during the observation period. Interviewing nurses other than those observed would require that rapport establishing process to repeated.