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With any research endeavor, it is crucial to ask yourself as many questions as possible to ensure you are thinking critically about the subject. For target market research, consider not just the age, but the lifestyle, gender, household size, location, culture, and other factors that would influence their behavior as a "consumer". Alternate your focus between your client's "product" (i.e., your Career Services event) and the "consumer" (i.e., potential attendees): Who would go to X event? Would student Y attend? What might prevent them from attending? How could the ad or client accommodate or change this behavior?
As you research, look for data/information that answers these questions. If you have trouble finding data/information to support your theory, you may be asking the wrong questions, or are trying to shoehorn data to support an answer that you created from the start. Let the research process guide you to the answer rather than begin your research with an answer in mind.