Content analysis is used to systematically summarize written, spoken, or visual communication in a quantitative way. The technique can be applied to existing material or to new data. Content analysis is also a way to code responses to open-ended questions. Both the content (meaning) and format (structure) of a communication are subject to analysis. Because it is usually less subjective, format tends to be easier to code than content.
Once the materials to be coded have been selected, a decision rule is made regarding the selection (sampling) of the material to be included in the analysis. The unit of measurement needs to be specified. The most difficult part of a content analysis is setting up the coding procedure -- how the information will be classified. There must be a clear specification of the coding categories and the procedure.
Categories must be comprehensive, mutually-exclusive, and non-instances may need to be recorded (for completeness). For reliability, two people independently coding the information should show a high degree of agreement in their classifications.
Content analysis is a versatile, unobtrusive and inexpensive research method. It is useful for documenting change over time, and comparing media from different sources and locations. It is easy to establish reliability. Materials tend to be easy to obtain. With regard to limitations, the method is purely descriptive and doesn't address why information is in the form shown. The information available for content analysis may not be representative of events or behavior.