In the study with smoking and diabetes external validity and Hawthorne bias is used to in the association of diabetes and smoking comparing a group of individuals with diabetes cases to the control a group of full-time hospital volunteers without diabetes who were full time employers of the same hospital. External validity is used in this case to generalize cases and control by associating them with diabetes and smoking to show a generalization between non smokers who have diabetes are healthier verse smokers who have diabetes that are hospitalized. Hawthorne bias is used in this case study because full time employees who volunteer to be controls can change their behavior at any time because they are in a study. For example the full time who
