Research and Evaluation Practice Test

Coverage bias shows up when the sampling frame doesn’t include every element of the population, so some individuals can’t be chosen at all. That gap means the resulting sample may systematically miss whole groups, making the estimates slide away from what’s truly happening in the population. For instance, using a directory of landline numbers as a frame can underrepresent younger people or those without landlines, skewing results. The other biases don’t fit this specific issue: selection bias comes from nonrandom choices within the frame itself, attrition bias from people dropping out over time, and measurement bias from errors in how data are collected, not from the frame’s incomplete coverage.