Instrumental Case Study — Issue-Driven Case Research

In an intrinsic case study the researcher is drawn to the case because of its own particularity — its uniqueness, its rarity, or its intrinsic interest. In an instrumental case study the case is studied because it promises to illuminate an external issue or theoretical question. The case is a means, not an end. This distinction shapes everything from how the case is selected (theoretical relevance vs. intrinsic interest) to how findings are framed (what the case teaches about the issue vs. what the case is like).

Both Stake and Yin are major theorists of case study research, but they emphasise different things. Yin (2014, Case Study Research) defines case study as a research strategy suited to 'how' and 'why' questions and places heavy emphasis on research design rigour and replication logic across cases. Stake focuses on the epistemological relationship between researcher and case, distinguishes intrinsic from instrumental purposes, and foregrounds naturalistic generalisation and thick description. Instrumental case study is Stake's concept; Yin's framework does not use that label, though his explanatory case study designs pursue similar goals.

A single case is sufficient when it is particularly illuminating, accessible, and richly documented. Multiple cases — Stake calls this a collective or multiple instrumental case study — are preferable when cross-case comparison is expected to deepen insight into the issue. There is no fixed minimum, but each additional case adds analytic burden; three to five cases is a common and workable range for collective designs. The criterion is theoretical saturation of the issue, not a numerical target.

Naturalistic generalisation, a term coined by Stake, refers to conclusions that readers reach for themselves by recognising that a case's circumstances and findings resemble situations they know from their own experience. It is not statistical generalisation from a sample to a population; it is inferential transfer grounded in the richness and credibility of case description. Most methodologists accept it as a legitimate form of knowledge claim in qualitative research, provided the case description is sufficiently thick and the researcher is transparent about the boundaries of the claim.

Yes. Instrumental case study is a research design, not a data-collection method. It is primarily qualitative but can incorporate quantitative evidence — survey scores, administrative records, outcome measures — as part of its multi-source triangulation strategy. What matters is that the quantitative data are interpreted in service of illuminating the issue within the bounded case context, not used for statistical generalisation.