In the survey results, the values displayed in the error bars represent the modeled margin of error: if we repeat this survey many times in the same way, 95% of the time, the resulting range of values would contain the true value.
In this example, the modeled margin of error for Basketball is +1.8%/-1.6%. The range of values is 12.4% to 15.8%; i.e., 14% adjusted by the modeled margin of error.
We follow the Pew Research Center in using the term "modeled margin of error" to differentiate from the statistical term "margin of error," which only applies to true probability-based samples. Because Google Surveys collects online non-probability samples, the margin of error calculation is based on assumptions about the Google Surveys sampling model and what would happen if we repeated the same sampling process many times. See this whitepaper for more details.
Four factors influence and can reduce the size of the modeled margin of error:
- Larger sample sizes
- Percentages closer to the extremes of 0% or 100%
- Lower confidence levels (we use a 95% confidence level)
- Lower variability of weights