The Population refers to the overall number of people in your target group, for instance, 2 million households in one country, 50000 nurses, etc. The Error Level refers to the accuracy of the survey questions and the Confidence Interval refers to accuracy of sampling the population. A typical value for the confidence is 95%, while the error is often set in the range 2-10%. More about these parameters can be found the User’s Guide of MM4XL software