In looking at this story, I was led to a recent Pew study that compared the political leanings of Twitter to the political opinions of the general US population. One takeaway: the two populations are not the same.

The lack of consistent correspondence between Twitter reaction and public opinion is partly a reflection of the fact that those who get news on Twitter – and particularly those who tweet news – are very different demographically from the public.

The overall reach of Twitter is modest. In the Pew Research Center’s 2012 biennial news consumption survey, just 13% of adults said they ever use Twitter or read Twitter messages; only 3% said they regularly or sometimes tweet or retweet news or news headlines on Twitter.

Twitter users are not representative of the public. Most notably, Twitter users are considerably younger than the general public and more likely to be Democrats or lean toward the Democratic Party. In the 2012 news consumption survey, half (50%) of adults who said they posted news on Twitter were younger than 30, compared with 23% of all adults. And 57% of those who posted news on Twitter were either Democrats or leaned Democratic, compared with 46% of the general public. (Another recent Pew Research Center survey provides even more detail on who uses Twitter and other social media.)

In another respect, the Twitter audience also is broader than the sample of a traditional national survey. People under the age of 18 can participate in Twitter conversations, while national surveys are limited to adults 18 and older. Similarly, Twitter conversations also may include those living outside the United States.

Perhaps most important, the Twitter users who choose to share their views on events vary with the topics in the news. Those who tweeted about the California same-sex marriage ruling were likely not the same group as those who tweeted about Obama’s inaugural or Romney’s selection of Paul Ryan.

This leads to me to three thoughts:

1. What does this mean for the archiving of Twitter being undertaken by the Library of Congress? While it is still an interesting data source, Twitter provides a very small slice of U.S. opinion.

2. This is emblematic of larger issues with relying on new technologies to do research: who uses newer technologies is not the same as the U.S. population. This can be corrected for, as a recent article titled “A More Perfect Poll” suggests, and technologies can eventually filter throughout the whole U.S. population. In the meantime, researchers need to be careful about what they conclude.

3. So…what do we do about a comparison of a non-representative sample to a population? Pew seems to admit this:

While this provides an interesting look into how communities of interest respond to different circumstances, it does not reliably correlate with the overall reaction of adults nationwide.

This is an odd way to conclude a statistical report.