Self-selection bias is a common type of bias in market research. Self-selection bias in market research is a type of non-sampling error in which the respondents who complete a survey are demographically or behaviorally different than the intended sample. This type of sampling bias has become more of an issue in recent years due to the popularity of social media and river sampling (all-in) methodologies to recruit as many people as possible to participate in market research studies.
River samples are essentially what they sound like. Using a multitude of different channels (social media, email, websites, etc.) to funnel survey respondents to one survey link. As response rates decline, multi-sampling approaches are often required to obtain the completes you need for your study if an online panel company cannot help.
Self-selection bias can occur in many forms. Here are some examples:
- A national retail store wants to understand satisfaction levels with in-store experiences. A link to a customer satisfaction survey is posted on the store's website. Those who take the survey are inherently more likely to be website visitors, spend more time online, and make more online purchases than respondents who do not visit the site to view the link. In-store customers may, and probably will exhibit different satisfaction scores than these website visitors.
- A local gym wants to conduct a short survey with the community to determine the best use of additional land which was purchased adjacent to its location. The link is shared on Facebook by the gym owner. The local high school soccer team captain sees the link and shares it on his Facebook page, the high school soccer team page, and shares it with other team captains in the area encouraging them to pick "soccer field" when asked what the best use of the land will be. Obviously this sample base of respondents will differ quite a bit from the average gym-goers' views on the additional property.
- A fairly common type of self-selection bias is evident with SAT and SAT prep courses taken by high school students. Results show SAT scores are higher for those who opt to take an SAT prep course. Therefore the course is credited as the reason students produce higher scores on the SAT. However, self-selection bias may be to blame because the "type" of student who takes an SAT course may be smarter, more-studious, or more logical than a student who chooses not to take the course. So the real reason the course results in higher average SAT scores could be driven by the types of students who opt into the course rather than the prep course itself.
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