Cadeliin, this is not Cognisonance work. This is research done by Pew Research. Though I'm not a Statistician, I've take four college level Statistic courses, and they have followed acceptable guidelines. In fact they did take a large sample, therefore the information is "more meaningful".
"The size of the national sample is unusually large for a religion survey. There are two main reasons for this. First, the large sample size makes it possible to estimate the religious composition of the U.S. with a high degree of precision. After taking into account the survey’s design effect (based on the sample design and the survey weights), the margin of error for results based on the full sample is +/- 0.6 percentage points.
Second, the large sample size makes it possible to describe the demographic characteristics of a wide variety of religious groups, including relatively small groups that cannot be analyzed using data from smaller surveys. With more than 35,000 respondents in total, the Religious Landscape Study includes interviews with roughly 350 people in religious groups that account for just 1% of the U.S. population, and with 100 or more people in religious groups that are as small as three-tenths of 1% of the overall population. For instance, the study includes interviews with 245 Jehovah’s Witnesses, a group that accounts for less than 1% of the U.S. population and is typically represented by only a few dozen respondents in smaller surveys."