What is the problem you are trying to solve?
This will become your research question. It will be used, along with background research, to develop your hypothesis.
What population does that problem primarily involve?
Applicable population: The population that you are studying in your project
Ask: What population are you studying in your experiment? Why?
Your choice of subject will be determined by convenience/accessibility of your subject population and by how a specific subject population fits the parameters of your research (think of this as how much the population provides crucial information for your experiment).
Ways of thinking about your applicable population:
age range (teenagers (13-18), young adults (18-25), mature adults (65+)
lifestyle characteristics (college students, early college students, basketball players, eldest siblings, etc.)
regional, cultural, and/or ethnic background (urban high school students, Eastern North Carolina residents, Haitian immigrants, Hispanic men, African-American college students, etc.)
Variables:
Independent vs Dependent Variables: What's the Difference?
Independent Variable: remains constant regardless of other factors in experiment (does NOT change)
Dependent Variable: changes based on other factors in experiment (should change)