Which Audience Analysis Measurements Principles and Techniques are Most Effective and Why?

When choosing between the variety of analysis measurement principles for audiences I would say probability sampling is the most effective. With probability sampling you have complete control over your sampling, you can choose the number of people in your sample and the confidence level of the results so you can clearly articulate that "evidence shows that at a 95% confidence level the results are..." there is no question to wether or not you are accurate because you can also do statistical analysis to show how close your sampling results would be to the mean. Unless a company does it for themselves and picks a select group more favorable to them, but if the test is done fairly and properly, it is the most effective.