Furthermore, defining peer relationships is very difficult. Friendship groups change over time and people may associate with different people for different activities. In research into social norms, for example, it may be that students are more accurate in their perception of their best friends’ drinking habits than they are of others’, and therefore using the term ‘peer influence’ is too broad. This is therefore a limitation of this explanation in that friendship groups do not remain stable, they change and this can pose a problem for research in this field.