Search around for ways to make a little extra money online, and you might find yourself at one of many sites that offer to pay you to take surveys.

There’s Swagbucks, SurveyJunkie, InboxDollars, and KashKick, for instance. On each of these sites, users are paid small amounts of money for completing surveys, playing games, or making purchases.

The surveys on these sites are “opt-in” surveys, meaning that participants are actively choosing to take them, rather than researchers pulling a random sample of a population to poll, as professional pollsters do.

Unsurprisingly, opt-in surveys can lead to some skewed results: earlier this week Pew Research Center wrote about their analysis of one such opt-in survey that found 20 percent of US adults under 30 believe that “The Holocaust is a myth.” Pew’s attempt to replicate this result via a random sampling of Americans found that just 3 percent of Americans under 30 agreed with an identically worded statement about the Holocaust — a percentage that was more or less the same across all age groups.

The analysis also included this incredible tidbit:

“In a February 2022 survey experiment, we asked opt-in respondents if they were licensed to operate a class SSGN (nuclear) submarine. In the opt-in survey, 12% of adults under 30 claimed this qualification, significantly higher than the share among older respondents. In reality, the share of Americans with this type of submarine license rounds to 0%.”

Oof, right?

The Google results for survey sites are filled with reviews from people who are mainly concerned with whether these sites are “legitimate” or scams. But the Pew analysis points to another question: just how good is the data collected for a survey when its participants are incentivized to speed through as many as possible in order to earn cash?

The problems with opt-in surveys, explained

I dug around and, surprise! It’s complicated.

“Errors are introduced (and remediated) in the survey process at every step,” noted David Rothschild, an economist at Microsoft Research. The fact that a survey was conducted online for a small reward isn’t necessarily enough information to analyze data quality in a meaningful way.

As Pew noted in its analysis, the Holocaust denial survey used an agree/disagree format that can lead to “acquiescence bias” — a tendency for respondents to give an affirmative reply. This means that while the survey collection method might have been part of the problem, the question itself may have also led to inaccurate results.

“There are many types of opt-in online audiences; some have strong vetting to ensure the respondents are who they say they are and produce high quality responses, while others just accept whomever without any pre-response quality control,” Rothschild added.

Here’s what you need to know.

How do online survey sites work?

Although there are a couple different models, the online survey sites we are talking about offer small rewards in exchange for survey participation. Most say they try to “match” users to relevant surveys based on the data they collect about their users, and generally speaking, you only get paid if you qualify to take the survey and complete each required question.

Typically, these sites pay users in points, which translate to small dollar amounts per survey, if they pass a set of screening questions and complete the entire survey. These points often do not translate to very much money: I created an account on Swagbucks and checked a list of available surveys. They included a 20-minute survey for 119 “Swagbucks,” which translates to … $1.19.

Longer surveys may offer more, while some surveys with a 10-minute time estimate offer less than a dollar. These are similar to the rates I saw on SurveyJunkie. On Amazon’s Mechanical Turk, a marketplace for work that includes survey taking, a survey might pay less than 10 cents.

Why would pollsters and researchers use sites like these to collect responses?

In some applications like election polls, as Pew noted, opt-in surveys can perform similarly to random probability-based surveys. Which is great, because they are generally much cheaper to conduct.

“Lower cost survey pools are great for exploration” and when you don’t need a very precise outcome, said Rothschild. The results are generally faster, cheaper, and more convenient.

“Especially for research that’s being done on a close-to-shoestring budget, opt-in online surveys are a natural choice for scholars trying to study diverse aspects of social behavior,” added Thomas Gift, an associate professor of political science at University College London.

Gift and another researcher studied the potential of fraudulent responses in online opt-in studies after using an opt-in study themselves to study a separate question. “It was only during the fielding of the experiment that large cohorts of respondents seemed to be giving suspicious answers about their backgrounds,” he said. “So we investigated further.”

Why, and when, are online surveys prone to bogus respondents?

Researchers can use a lot of tools, including screening questions, to weed out bad responses and end up with a set of usable data. But there are some instances, such as obscure beliefs or surveys where you need really precise data, where opt-in online surveys are going to be a problem.

Pew noted a few considerations here: based on their research over the years, online opt-in polls have a tendency to overestimate fringe beliefs (they gave the example of belief in conspiracy theories). That overrepresentation is more severe among younger respondents, and among Hispanic adults, they noted.

Gift and his research partner hired a “nationally-recognized” marketing firm — which they left unnamed in their paper for liability reasons — to conduct a survey for them that collected respondents with experience in the Army. This firm, they said, distributed the survey to a number of sub-vendors that provided financial incentives for responses (these sub-vendors were also left anonymous).

In order to detect whether respondents really did have experience in the Army or not, Gift used screening questions embedded in the survey. Respondents were asked about saluting protocol, and for specific information on their military background.

Based on their analysis of those screeners, nearly 82 percent of respondents may have pretended to be associated with the Army in order to take the survey and get paid for it. About 36 percent of those respondents passed the knowledge screening test, but were identified as probably misrepresenting themselves based on their answers to the survey questions themselves.

And there was also evidence in the survey results that some respondents were taking the survey a bunch of times, giving nearly identical answers and tweaking their demographic data enough to pass as different people, presumably to get paid multiple times for the same survey.

How can researchers minimize bogus responses and end up with useful data from an online survey?

Essentially, by testing the respondent. Online surveys use attention checks, IP tracking, anti-bot software, and monitoring the time it takes for someone to complete a survey in order to try to mitigate fraud. Asking respondents questions like the one Pew flagged about having a license to drive a submarine is a pretty good way to tell whether someone is just cruising through and answering questions as quickly as possible, or if they’re actually reading the questions.

Nothing is going to catch every single bogus response, and, as Rothschild noted, some low-quality responses will slip through attention checks.

There are also other models for collecting data online, Gift noted. Opt-in volunteer surveys “aren’t without their limitations,” but they create a different set of incentives for participants that don’t rely on a financial reward. Gift highlighted the work of the Harvard Digital Lab for Social Sciences, an online platform that allows people to volunteer to participate in social science research.

While researchers might not be able to catch every single bad response, they can be transparent about how they collected their data, Rothschild noted. And it’s worth looking for that information the next time you see a shocking headline about a shocking belief held by The Youth.