External Validity External validity means the results of the experiment can be generalized to the target population. For example, imagine that a food company wants to find out if its new dessert would appeal to a market segment between the ages of 18 and 35. It would be too costly to ask every 18- to 35-year-old in the United States to taste the product. But using experimental design methods the company can randomly select individuals in the target population (ages 18–35) and assign them to different treatment groups, varying one component of the dessert for each group. Respondents in each treatment group would then taste the new dessert. If 60 percent of the respondents indicated they would purchase the product, and if in fact 60 percent of the targeted population did purchase the new product when it was marketed, then the results of the study would be considered externally valid. Random selection of subjects and random assignment to treatment conditions are usually necessary for external validity, but they are not necessarily sufficient to confirm that the findings can be generalized.