What is an adequate sample size?

TY - JOUR

T1 - What is an adequate sample size?

T2 - Operationalising data saturation for theory-based interview studies

A1 - Francis,Jill J.

A1 - Johnston,Marie

A1 - Robertson,Clare

A1 - Glidewell,Liz

A1 - Entwistle,Vikki

A1 - Eccles,Martin P.

A1 - Grimshaw,Jeremy M.

AU - Francis,Jill J.

AU - Johnston,Marie

AU - Robertson,Clare

AU - Glidewell,Liz

AU - Entwistle,Vikki

AU - Eccles,Martin P.

AU - Grimshaw,Jeremy M.

PY - 2010

Y1 - 2010

N2 - <p>In interview studies, sample size is often justified by interviewing participants until reaching 'data saturation'. However, there is no agreed method of establishing this. We propose principles for deciding saturation in theory-based interview studies (where conceptual categories are pre-established by existing theory). First, specify a minimum sample size for initial analysis (initial analysis sample). Second, specify how many more interviews will be conducted without new ideas emerging (stopping criterion). We demonstrate these principles in two studies, based on the theory of planned behaviour, designed to identify three belief categories (Behavioural, Normative and Control), using an initial analysis sample of 10 and stopping criterion of 3. Study 1 (retrospective analysis of existing data) identified 84 shared beliefs of 14 general medical practitioners about managing patients with sore throat without prescribing antibiotics. The criterion for saturation was achieved for Normative beliefs but not for other beliefs or studywise saturation. In Study 2 (prospective analysis), 17 relatives of people with Paget's disease of the bone reported 44 shared beliefs about taking genetic testing. Studywise data saturation was achieved at interview 17. We propose specification of these principles for reporting data saturation in theory-based interview studies. The principles may be adaptable for other types of studies.</p>

AB - <p>In interview studies, sample size is often justified by interviewing participants until reaching 'data saturation'. However, there is no agreed method of establishing this. We propose principles for deciding saturation in theory-based interview studies (where conceptual categories are pre-established by existing theory). First, specify a minimum sample size for initial analysis (initial analysis sample). Second, specify how many more interviews will be conducted without new ideas emerging (stopping criterion). We demonstrate these principles in two studies, based on the theory of planned behaviour, designed to identify three belief categories (Behavioural, Normative and Control), using an initial analysis sample of 10 and stopping criterion of 3. Study 1 (retrospective analysis of existing data) identified 84 shared beliefs of 14 general medical practitioners about managing patients with sore throat without prescribing antibiotics. The criterion for saturation was achieved for Normative beliefs but not for other beliefs or studywise saturation. In Study 2 (prospective analysis), 17 relatives of people with Paget's disease of the bone reported 44 shared beliefs about taking genetic testing. Studywise data saturation was achieved at interview 17. We propose specification of these principles for reporting data saturation in theory-based interview studies. The principles may be adaptable for other types of studies.</p>

KW - data saturation

KW - sample size

KW - interviews as topic

KW - models

KW - psychological

KW - theory-based content analysis

KW - PLANNED BEHAVIOR

KW - HEALTH

KW - PROFESSIONALS

KW - CONSULTATIONS

KW - COMMUNITY

KW - RESOURCE

KW - PEOPLE

KW - ACCESS

KW - CARE

UR - http://www.scopus.com/inward/record.url?partnerID=yv4JPVwI&eid=2-s2.0-78649552441&md5=94a9716cd6562ae2792395acef3ce9df

U2 - 10.1080/08870440903194015

DO - 10.1080/08870440903194015

M1 - Article

JO - Psychology and Health

JF - Psychology and Health

SN - 0887-0446

IS - 10

VL - 25

SP - 1229

EP - 1245

ER -