You are a clinical psychologist and you have a 14-year-old female client who you believe has bulimia nervosa (binging and purging food), but your client will not admit the problem and you have very little evidence to support your assumptions. you decide you need to collect information from family, friends, and teachers. you hope to interview these people about your client and to ask them to report any behavior that may reflect your diagnosis. you also want to record her eating habits and weight over the next two weeks. you hope the information you collect will you become better with this type of diagnosis with future patients. this intensive investigation of your client is called a(n):