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Statistical Accuracy of a Survey

The chart below is used for determining accuracy of a survey sample. 

Let's say we have an accuracy of +/- 10%, and our questions use an interval scale that ranges from 0 to 5 (so there are 5 equal intervals in the scale).  Let's say we get sufficient responses so we're on the +/-10% curve.  Plus or minus 10% on our scale is 1 full interval point (20% of 5).  
Therefore, we can say that if we got responses from everyone in the population, we are 95% certain that average (the population mean) would lie within a band of 1 point on our scale with the average score from a survey question (the sample mean) in the middle.  Put a different way, if that survey question had a mean score of 3.5, then we are fairly certain that if we conducted a census, the score found would lie in a band from 3.0 to 4.0.  

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