One of the first things taught in physics experiments in school is to identify the assumption you are making. Unfortunately this step is often overlooked in business. It is almost impossible to avoid making assumptions in almost any business situation because:

Some information is incomplete ... it simply may not available. For example: The launch strategy for your competitors new product or final product features in you are in a pre-production phase
There may not be enough time to collect all the data
Covering absolutely everything could cause a smoke screen so that you loose track of the major purpose

The real issue is that you cannot place complete reliance on your conclusions unless you understand the complete picture.

It is also important to clearly state the purpose of this analysis. Ideally this should be in terms of Aims & Objectives ... but it is not always necessary to be quite so formal. Remember:

If you don\"t know where you are going, don\"t be surprised if you don\"t get there!
An \"Aim\" is an unambiguous statement of purpose
An \"Objective\" is an action needed to achieve the aim and has three components: The performance required, the conditions under which that performance occurs and the standard to be achieved.
Unless you have some statement containing quantity/and or due dates it is very difficult to measure successful outcomes

Strategic Planning