What is the margin of error?

• A. The statistically calculated difference between the test result and the theoretical result if a larger population were tested
• B. The difference between two observed conversion rates
• C. The standard deviation of daily impressions
• D. The percentage of tests that failed

Answer: (A)

Understanding margin of error means recognizing how far your sample estimate could be from the true population value due to sampling randomness. The margin of error is the statistically calculated difference between the test result and what we would expect if we could test a larger population, typically shown as ± a certain percentage at a chosen confidence level. This is exactly what the option describes. The other choices don’t fit: the difference between two observed conversion rates compares two samples rather than estimating how far a single sample might be from the population value; the standard deviation of daily impressions measures data spread, not sampling error in an estimate; and the percentage of tests that failed is simply a failure rate, not an estimate of how far the result could deviate from the population truth.