Sampling Frame vs Population
Both terms below come up in the same part of the course, and students mix them up. Here is each one defined on its own, side by side, so you can see where they part company.
Sampling frame
Collecting data and study design
A sampling frame is the actual list of individuals a sample is drawn from; when it misses part of the population, undercoverage results.
The population is who you want to describe, and the frame is who your method can actually reach. A town survey that dials numbers from a landline directory has a frame that excludes cell-only households, so those adults have zero chance of selection. Any group missing from the frame is missing from every sample you draw, and a larger sample does not fix that gap. Asking who the frame can never reach is the first question worth putting to any survey.
Population
Collecting data and study design
A population is the entire group of individuals or objects you want to study and draw conclusions about.
A population includes every member of the group in question, not just the ones you happen to observe. For example, if you want the average height of all students at a school, the population is all of those students, and its true mean height is a fixed number you usually cannot measure directly. A numerical fact about a population, such as the population mean (the Greek letter mu, written ), is called a parameter. You typically estimate it from a smaller sample.