Glossary
Research sampling glossary.
Plain, accurate definitions of the terms we use when we build a sample frame — coverage, denominators, provenance, lawful basis, and the rest.
Sampling frame
The list of all units from which a sample is actually drawn — ideally, every member of the population you want to study. The quality of any study is capped by the quality of its frame: you can only generalise to what the frame contains.
Sample frame
The term widely used in commercial research for a constructed, screened list of a defined population, built for a specific study. In practice it means the same as a sampling frame, with the emphasis on being purpose-built rather than borrowed from an existing pool.
Coverage (in sampling)
The degree to which a frame includes the population it is meant to represent — what proportion of real members actually appear in it. Coverage is only meaningful when stated against a known total, which is why it is always expressed relative to a denominator.
Coverage statement
An explicit, checkable claim about how much of a defined population a frame reaches — typically “n members identified against a denominator of N, equal to X%.” It names the population, the authoritative source of the denominator, and shows the arithmetic.
Denominator
The total size of the population you measure coverage against — the N in “n out of N.” Its credibility depends on its source: a denominator drawn from an authoritative registry is defensible; one estimated informally is not.
Incidence rate
The proportion of a general or sampled audience that belongs to your target population. Low incidence is what makes a population “hard to reach”: the rarer the target, the more it costs a panel to find each qualifying respondent.
Low-incidence sample
A sample targeting a population that appears only rarely in the general or panel base, making it disproportionately expensive and unreliable to reach through standard quotas. For these populations a constructed, screened frame is usually both more accurate and more economical.
Provenance
The documented origin of each record: where the person was identified and why they belong in the frame. Provenance is what lets a frame withstand the question “where did this come from?” — for a client, an ethics board, or a regulator.
Evidence-anchored record
A record that carries a specific source reference — typically an evidence URL — showing exactly where the individual was identified as a member of the population. It moves a record from “trust us” to “see for yourself.”
Registry-anchored
A frame is registry-anchored when both its membership criteria and its coverage denominator are tied to an authoritative register of the population. Anchoring to a registry is what makes a coverage figure defensible rather than self-graded.
Screening
Confirming that each candidate genuinely meets the population’s definition before they enter the frame or study. The lower the incidence, the more screening rigour matters, because the cost of a false positive rises sharply.
Fitness-to-study
Whether a given individual meets the requirements of this particular study — the specific inclusion criteria, quotas, and ethical conditions of the project, not just the broad population. Checking it before fieldwork prevents wasted completes.
Legitimate interests (research)
One of the lawful bases for processing personal data under the UK GDPR, available where processing is necessary for a genuine interest, balanced against the rights of the individual. For bona fide research recruitment it can be appropriate, provided the interest is documented and individuals can object.
PECR
The Privacy and Electronic Communications Regulations govern electronic communications in the UK — including who may be contacted and on what basis — and sit alongside GDPR. It matters because how participants are approached must be lawful, not only how their data is held.
Suppression list
A record of individuals who must not be contacted or included — because they have objected, withdrawn, or exercised their rights. Applying suppression before delivery ensures a frame honours prior opt-outs.
Data subject rights
The protections individuals hold over their personal data under GDPR — to be informed, to access, to rectify, to erase, and to object. Honouring these rights is an ongoing obligation, and a credible frame is built so requests can be actioned promptly.
Hard-to-reach population
A population that standard sampling methods struggle to access — usually because of low incidence, niche professional definition, or absence from conventional panels. Reaching them well depends less on volume than on precise definition, screening, and provenance.
Transnational education (TNE)
Education delivered by an institution to students based in a different country from the awarding body — for example a UK degree taught through an overseas partner or branch campus. Its professionals are a textbook hard-to-reach population: defined, dispersed, and largely absent from standard panels.