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."