Advantages & Disadvantages of Analysing Written Documents for the Purposes of Research
One of the key advantages in conducting documentary research is that you can get access to information that would be difficult to get in any other way, such as people or cases who might not be willing to talk in a formal research interview or might be difficult to track down. By using documents you eliminate the effect that you, as an individual, have on a person or situation when you conduct research ('the researcher effect'). The effect you have on a situation or subject may be partly due to the knowledge that you are there as a researcher. People will also be affected by how you conduct yourself and how they perceive you. Issues of sex, age, race and other characteristics are likely to have an impact on what people tell you or do when they know they are being researched.
Documents are often particularly useful for tracking change over time; that is, doing longitudinal research. Longitudinal research may be done either prospectively (forward) or retrospectively (back over time). Documents often make possible the collection of data over a longer period of time as well as larger samples than might be collected from questionnaires or interviews. Some documents may contain spontaneous data, such as feelings, and refer to actions that are recorded in a specific context, not with a view to answering a particular research question. Confessional documents may give us an insight into how people see things or how they want to present things. Either way, they provide a very particular account of reality whatever the confessor's motivation behind their account.
Further advantages of using documents in research include the fact that such research is relatively low cost, particularly when the documents are easily accessible and already located in your workplace, or on the internet. Documents vary a great deal in quality, often related to the perceived importance of recording certain information, but some types of document can be extremely detailed and yield much more information than you could hope to gain from a questionnaire or interview.
Nevertheless, documents are usually not designed with research in mind. The information recorded may be idiosyncratic or incomplete. Documents get misfiled, left on people's desks for long periods or simply just do not get fully completed at all. Even standard ways of collecting data in a police station may change, so there may be information that is available for one period of time and not another. All of this will create gaps in data (missing data) as well as coding difficulties. The motivation to collect certain types of data will vary over time, perhaps related to the decision by a particular team to focus on a specific issue for a period of time or because of government targets.
Many of the above advantages and disadvantages apply to other secondary sources, but they vary a great deal with the type of source.