When comparing percentages, it can accordingly be useful to consider the probability that one percentage is higher than another.  In simple situations, this probability can be derived with 1) the standard error calculation introduced earlier, 2) the formula for the variance of the difference of two random variables , and 3) an assumption that if anyone does not choose Kerry they will choose Bush, and vice versa; they are perfectly negatively correlated . This may not be a tenable assumption when there are more than two possible poll responses. For more complex survey designs, different formulas for calculating the standard error of difference must be used.
Many people feel that sans serif fonts look “cleaner” and more “modern,” while serif fonts look more traditional, more book-like. The conventional wisdom has been that serif fonts are more readable—particularly in print—while sans serif fonts are more legible. If you have to read large blocks of text, the serifs at the ends of letters makes them easier to identify and easier to read. On the other hand, the simplicity of Sans Serif fonts are thought to make these fonts more legible and easier to read in small sizes or on coarse screens. For these reason, you see lots and lots of sans serif fonts on web pages.