While diagnosis is a common term among practitioners, it holds the connotation of the doctor–patient consulting. It is during the diagnosis and feedback phases that the consultant and the client explore a more thorough and nuanced view of the problem, a view that has been only partial to the client up to this point. Different interpretations of problems exist depending on job roles, organizational locations, individual experiences, and understanding this can help consultants and clients attack causes the of problems, rather than symptoms.

Practitioners often make two common mistakes in the diagnosis phase. Diagnosis is not a conclusion to come to in one day, but a set of preliminary beliefs about what is generally happening to be adapted as the organization changes. Practitioners often make the mistake of single-handedly shouldering the burden of diagnosis. Instead, diagnosis ideally would involve clients or even client teams in the process.

The diagnostic phase consists of a number of interrelated activities. Analyze the data. The consultant must summarize and abstract key points from the data. The consultant will look for common themes in the data and organize them in a way that helps the client understand the problem. Interpret the data. Interpreting means drawing conclusions that are supported by the data. The consultant’s role is to present the facts as well as to facilitate understanding and implications of the interpretations.

Select and prioritize the right issues. Almost all data gathering activities will produce a long list of issues. Selecting those that are most energizing will help the client to be motivated to focus on a narrow set of issues to be addressed. The issues will not all have equal relevance or contribution to the problem, so the consultant can help the client to see which issues may have higher impact or priority than others.