This same approach can be used to predict other demographic variables, such as age and income. For instance, The Wall Street Journal conducts surveys to learn about income levels and a variety of other characteristics of its subscribers. So, if clickstream data show a person visited WSJ.com. we can infer something about that person's income level. Of course, questions about privacy are a major issue using these techniques
*Based on Alan Montgomery, "Applying Quantitative Marketing Techniques to the Internet." Interfaces (March/April 2001): 90-108.