One issue, that most sociologists encounter when conducting research, is the need to operationalise concepts: to make them measurable. For example, social class is often a key concept in sociological research, but how do researchers choose to measure and categorise class? They can use occupation categories, household income or how people identify themselves, and they would all be very different and therefore garner very different results. Concepts like "social cohesion" can be even harder to turn into measurable data.