What is Coverage Error Rate?
Coverage error rate is the share of the target population that is excluded from your survey’s sampling frame. It measures how much of the group you want to hear from isn’t actually reachable by the way you’ve set up or distributed the survey.
Coverage error occurs when some members of the population of interest have zero chance (or a much lower chance) of being included in the survey because of how the sample frame, mode, language or distribution is chosen. The coverage error rate expresses that as a percentage: (Number of people in the target population not covered ÷ Total target population) × 100. For non-experts: if the people you want to hear from aren’t able to see or access your form — for example because it’s only in English or only distributed via channels some communities don’t use — that gap is coverage error.
Usage example
A city council wants feedback from 10,000 residents. Their contact list includes phone numbers for 8,500 people, so the sampling frame coverage is 85% and the coverage error rate is 15% (1,500 residents not reached). In a different example, a school sends a parent survey only in English while 20% of parents speak a different primary language; the survey’s coverage error rate for non-English-speaking parents would be around 20% unless the survey is made available in those languages.
Practical application
Coverage error rate matters because it directly biases results and reduces the legitimacy of decisions based on those results. If whole communities — for example non-English speakers, people without internet access, or residents reached only by channels you didn’t use — are missing from the sample, findings will misrepresent needs and priorities. Practically, measuring and reducing coverage error helps you: - Identify which groups are excluded (by language, channel or geography) - Prioritise outreach or alternative collection methods (translated surveys, phone interviews, paper forms) - Decide whether weighting or follow-up sampling is needed - Demonstrate that consultations were inclusive and defensible Using a multilingual platform like Hearo can reduce coverage error by making a single survey accessible in many languages and by lowering the barrier for participation in under-reached communities.
FAQ
How is coverage error different from nonresponse error?
Coverage error happens when people never have a chance to be in the sample because of the sampling frame or distribution method. Nonresponse error happens when people who were reachable choose not to respond. Both bias results, but they have different solutions: reduce coverage error by changing how and where you reach people; reduce nonresponse error by improving engagement, reminders, incentives or survey design.
How do I calculate coverage error rate?
Estimate the number of people in your target population who are not included in your sampling frame, divide that by the total target population, and multiply by 100. For example, if 2,000 of 10,000 target residents are not reachable via your chosen channels, coverage error rate = (2,000 ÷ 10,000) × 100 = 20%.
What level of coverage error is acceptable?
There’s no universal threshold — acceptability depends on your objectives and who’s being excluded. Small, random gaps may be tolerable for exploratory work, but if excluded groups are systematically different (e.g., by language, income, or location), even a small coverage error can be unacceptable. The safest approach is to try to keep coverage error as low as feasible and to document who was excluded and why.
Can multilingual surveys eliminate coverage error?
Making a survey available in the languages your community uses significantly reduces coverage error related to language barriers, but it won’t fix other causes (like lack of internet access or outdated contact lists). Multilingual tools like Hearo remove a major source of exclusion by allowing one survey to reach more people, and combined with multiple distribution modes they substantially lower overall coverage error.