In accordance with fundamental humanitarian principles, these decisions and subsequent humanitarian relief should be based on assessed needs. However organizations are, very often independently, gathering information to analyse the scale, geographical spread and impact of the disaster. In spite of the importance of collecting information on needs, currently no commonly accepted methodology for needs assessment exists within the humanitarian system.

Numerous methodologies have been developed by individual agencies and within sectors, but it is difficult to compare the results from these different assessments. This lack of coordination of needs assessment practice has weakened evidence based decision making and humanitarian response. The Tsunami Evaluation Coalition (TEC) Thematic Report on Needs Assessment noted that "little information on methodology was available to judge the validity of needs assessments reviewed" and went on to identify shortcomings such as the lack of a unique format for rapid assessments, the variable definition of who is affected and eligible for assistance and the tendency of assessments to ignore local coping capacity.

As a result, current practice suggests that initial decisions following a disaster are partly based on assumptions and analysis formed through prior experience and the use of data immediately available such as information delivered by initial assessments, media, witness, etc. Often these assumptions do not enough factor in existing information available at national, regional or global level such as demography, geography, vulnerabilities and risk profiles, baseline information, satellite imagery, remote sensing, etc.