These factors are from pp. 7-10 in Wes Perkins (Ed.). The Social Norms Approach to Preventing School and College Age Substance Abuse: A Handbook for Educators Counselors, and Clinicians (2003), Jossey-Base

• First, there is a stereotype that college students don’t just drink alcohol, they drink a lot. This assumption leads many people, particularly incoming students, to believe that it is the norm for college students to drink and drink heavily. Thus, when a college student is seen drinking, it is assumed that that student is drinking a lot. Are he or she, or is it just an assumption? This assumption can spill over at parties where alcohol is present. Perhaps there are some people drinking heavily, it’s verifiable. But does that mean everyone is drinking a lot? How often do people actually count the number of drinks a person is having? How often do people actually count the number of drinks everyone at a party is drinking? If one works off assumptions, then one may assume that more drinking is taking place than is actually being done. (If someone is a little loud and outgoing, it may be assumed that he or she is drunk, and he or she may not be. People at parties are often boisterous and gregarious even without consuming alcohol. Sometimes people who are not drunk will act drunk and even think they are drunk!). In summation, if we believe college students drink a lot, then we will see college students drink a lot as it fits our image but we won’t see those who are not drinking or drinking a lot, as it does not fit our perception.
  
• Second, Wes Perkins reports that there is a general social psychological tendency to mistakenly attribute observed behaviors of others to their disposition – we think that the behavior we see is typical of them when their behaviors cannot be explained by the specific context or put into perspective by knowing what others do most of the time. For example, if we see someone for the first time and that person is drunk, we often assume that this person must get drunk every time he or she drinks. We usually don’t take into consideration a specific context, like maybe this is an abnormal behavior for that person. Quoting Perkins, “We simply tend to assume that what we have observed of others on occasion is what they normally do if we have no concrete basis to think otherwise.” (p. 7). Naturally, this psychological tendency is true in observing other behaviors as well.
  
• Third, usually the people at parties that garner the most attention are those who are drunk or who may not be drunk but may be acting drunk. We don’t pay attention to the normal activity that goes on, like people talking quietly to each other. Like the news, if something is reported about the party at a later time, it is often abnormal behavior. And it can get reported enough to lead others to think that such behavior is more the norm than it actually is.
  
• Fourth, according to Perkins cultural media reaffirm and amplify these drunken exaggerations. Television, movies, and music frequently depict and give a positive view of substance abuse. This gives a slanted view as it presents a disproportional view – for example many of these movies show a lot more people using a lot more alcohol than is true for underage people in reality. However, many assume that these movies show “normal” use. News media and other community outlets give headline attention to problem behaviors of those underage and do not highlight the healthy majority. After all, as Perkins points out, the healthy majority is not seen as newsworthy. Typically it is the abnormal that captures the headlines.