Ashley Richards is a survey methodologist at RTI International. This post first appeared on SurveyPost on 29, July 2014.
We recently took this research a step further and compared the accuracy of these approaches to multiple imputation, with the help of our colleague Darryl Creel. Imputation is the approach traditionally used to account for missing data and we wanted to see how the nontraditional approaches stack up. Furthermore, we wanted to check out these approaches because imputation cannot be used in the case where survey questions are not asked. This commonly occurs because of space limitations, the desire to reduce respondent burden, or other factors. I will be presenting on this research at the upcoming Joint Statistical Meetings (JSM), in early August. I’ll give a brief summary here, but if you’d like more details on it please check out my presentation or email me for a copy of the paper.
Income was the only variable for which imputation was the most accurate approach, but the differences between imputation and the other approaches were not statistically significant. Imputation correctly predicted income 32% of the time, compared to 25% for human coders and 26% for the machine algorithm. Considering that there were four income categories and a person would have a 25% chance of randomly selecting the correct response, I am unimpressed with these success rates of 25%-32%.
Human coders outperformed imputation on the other demographic items (age and sex), but imputation was more accurate than the machine algorithm. For these variables, the human coders picked up on clues in respondents’ Tweets. I was one of the coders and found myself jumping to conclusions, but I did so with a pretty good rate of success. For instance, if a Tweeter said “haha” a lot or used smiley faces, I was more likely to guess the person was young and/or female. These are tendencies that I’ve observed personally but I’ve read about them too.
As a coder I struggled to predict respondents’ health and depression statuses, and this was evident in the results. Imputation was better than humans at predicting these, but the machine algorithm was even more accurate. The machine was also best at predicting who respondents voted for in the previous presidential election, with human coders in second place and imputation in last place. As a coder I found that predicting voting was fairly simple among the subset of respondents who Tweeted about politics. Many Tweeters avoided the subject altogether, but those who Tweeted about politics tended to make it obvious who they supported.
So what does this all mean? We found that even with a small set of respondents, Tweets can be used to produce estimates with accuracy in the same range or better as imputation procedures. There is quite a bit of room for improvement in our methods that could make them even more accurate. For example, we could use a larger sample of Tweets to train the machine algorithm and we could select human coders who are especially perceptive and detail-oriented. The finding that Tweets are as good or better as imputation is important because imputation cannot be used in the case where survey questions were not asked.
As interesting as these findings may be, they need to be taken with a grain of salt, especially because of our small sample size (n=29). Relying on Twitter data is challenging because many respondents are not on Twitter, and those who are on Twitter are not representative of the general population and may not be willing to share their Tweets for these purposes. Another challenge is the variation in Tweet content. For example, as I mentioned earlier, some people Tweet their political views while others stay away from the topic on Twitter.
Despite these limitations, Twitter may represent an important resource for estimating values that are desired but not asked for in a survey. Many of our survey respondents are dropping clues about these values across the Internet, and now it’s time to decide if and how to use them. How many clues have you dropped about yourself online? Is your online identity revealing of your true characteristics?!?
 Even if approaches using Tweets may be more accurate than imputation, they require more time and money and in many cases may not be worth the tradeoff. As discussed later, these findings need to be taken with a grain of salt.
 We had more than 2,000 respondents, but our sample size for this portion of the study was greatly reduced after excluding respondents who don’t use Twitter, respondents who did not authorize our use of their Tweets, and respondents whose Tweets were not in English. Furthermore, half of the remaining respondents’ Tweets were used to train the machine algorithm.