You'll find thousands of authoritative sources backing this suggestion.

Examples:

http://contamsites.landcareresearch.co.nz/risk_assessment_ti...
"Broadly, the ***degree of detail*** and quality of the data at each level can be described as:
Tier 1: Qualitative (Introductory Risk Assessment)
Tier 2: Semi-quantitative (Advanced Risk Assessment)
Tier 3: Quantitative (Advanced Risk Assessment)"

AND

"USEPA risk assessment methods do not explicitly provide a tiered approach but leave the decision to risk assessors. However, in New Zealand we believe that few risk assessments require the ***level of detail*** described in some US models. The Canadian and Australian models do provide for a tiered approach and, to allow for the range of site sizes and complexity commonly found in New Zealand, a tiered model is considered the most appropriate method of working through a risk assessment."

http://www.fao.org/docrep/006/y4302e/y4302e08.htm
"Defining the scope of the MRA will determine the ***degree of detail*** required. In the ideal situation, the exposure pathway developed in the MRA will cover the entire production-to-consumption continuum, and the scope will detail the specific consumer population(s) of concern, the adverse health end-point(s) that are of interest, and other aspects that will guide data collection, modelling, analysis, and presentation of results. Properly defining the scope will also provide insights as to the timeframe and resources that will be needed for the MRA."

http://www.chm.bris.ac.uk/safety/nfrass.htm
"Example

As an example of the style and ***degree of detail*** recommended in writing a Risk Assessment read that for the Transportation, Storage and Use of Compressed Gas Cylinders"