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A dynamic treatment regimen is a sequence of prespecified decision rules which can be used to guide the delivery of a sequence of treatments or interventions that is tailored to the changing needs of the individual. The sequential multiple-assignment randomized trial is a research tool which allows for the construction of effective dynamic treatment regimens. We derive easy-to-use formulae for computing the total sample size for three common two-stage sequential multiple-assignment randomized trial designs in which the primary aim is to compare mean end-of-study outcomes for two embedded dynamic treatment regimens which recommend different first-stage treatments. The formulae are derived in the context of a regression model which leverages information from a longitudinal outcome collected over the entire study. We show that the sample size formula for a sequential multiple-assignment randomized trial can be written as the product of the sample size formula for a standard two-arm randomized trial, a deflation factor that accounts for the increased statistical efficiency resulting from a longitudinal analysis, and an inflation factor that accounts for the design of a sequential multiple-assignment randomized trial. The sequential multiple-assignment randomized trial design inflation factor is typically a function of the anticipated probability of response to first-stage treatment. We review modeling and estimation for dynamic treatment regimen effect analyses using a longitudinal outcome from a sequential multiple-assignment randomized trial, as well as the estimation of standard errors. We also present estimators for the covariance matrix for a variety of common working correlation structures. Methods are motivated using the ENGAGE study, a sequential multiple-assignment randomized trial aimed at developing a dynamic treatment regimen for increasing motivation to attend treatments among alcohol- and cocaine-dependent patients. <\/jats:p>","DOI":"10.1177\/0962280219877520","type":"journal-article","created":{"date-parts":[[2019,10,1]],"date-time":"2019-10-01T11:20:55Z","timestamp":1569928855000},"page":"1891-1912","update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":21,"title":["Sample size considerations for comparing dynamic treatment regimens in a sequential multiple-assignment randomized trial with a continuous longitudinal outcome"],"prefix":"10.1177","volume":"29","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8367-0522","authenticated-orcid":false,"given":"Nicholas J","family":"Seewald","sequence":"first","affiliation":[{"name":"Department of Statistics, University of Michigan, Ann Arbor, MI, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kelley M","family":"Kidwell","sequence":"additional","affiliation":[{"name":"Department of Biostatistics, University of Michigan, Ann Arbor, MI, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Inbal","family":"Nahum-Shani","sequence":"additional","affiliation":[{"name":"Institute for Social Research, University of Michigan, Ann Arbor, MI, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tianshuang","family":"Wu","sequence":"additional","affiliation":[{"name":"AbbVie, North Chicago, IL, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"James R","family":"McKay","sequence":"additional","affiliation":[{"name":"Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Daniel","family":"Almirall","sequence":"additional","affiliation":[{"name":"Department of Statistics, University of Michigan, Ann Arbor, MI, USA"},{"name":"Institute for Social Research, University of Michigan, Ann Arbor, MI, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"179","published-online":{"date-parts":[[2019,10,1]]},"reference":[{"key":"bibr1-0962280219877520","volume-title":"Adaptive treatment strategies in practice","author":"Kosorok MR","year":"2016"},{"key":"bibr2-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1007\/978-1-4614-7428-9"},{"key":"bibr3-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1037\/a0039534"},{"key":"bibr4-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1002\/pds.3606"},{"key":"bibr5-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1002\/sim.6747"},{"key":"bibr6-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1007\/s13142-014-0265-0"},{"key":"bibr7-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1037\/a0029372"},{"key":"bibr8-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1111\/1467-985X.00154"},{"key":"bibr9-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1191\/1740774504cn002oa"},{"key":"bibr10-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1002\/sim.2022"},{"key":"bibr11-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1177\/1740774509344633"},{"key":"bibr12-0962280219877520","doi-asserted-by":"publisher","DOI":"10.1177\/1740774514525691"},{"key":"bibr13-0962280219877520","doi-asserted-by":"crossref","unstructured":"Thall PF. 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