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DESCRIPTION:Jack Bowden\, PhD\n\nProfessor\n	Department of Clinical and Biom
 edical Sciences |\n	University of Exeter\n\nWHEN: Wednesday\, November 20\,
  2024\, from 3:30 to 4:30 p.m.\n	WHERE: Hybrid | 2001 ºÃÉ«TVl College Avenue
 \, Room 1201\; Zoom\n	NOTE: Jack Bowden will be presenting from Exeter\n\nA
 bstract\n\nThe STEP 1 randomized trial evaluated the effect of taking sema
 glutide vs placebo on body weight over a 68 week duration. As with any stu
 dy evaluating an intervention delivered over a sustained period\, non-adhe
 rence was observed. This was addressed in the original trial analysis with
 in the Estimand Framework by viewing non-adherence as an intercurrent even
 t. The primary analysis applied a treatment policy strategy which viewed i
 t as an aspect of the treatment regimen\, and thus made no adjustment for 
 its presence. A supplementary analysis used a hypothetical strategy\, targ
 eting an estimand that would have been realised had all participants adher
 ed\, under the assumption that no post-baseline variables confounded adher
 ence and change in body weight. In this paper we propose an alternative In
 strumental Variable method to adjust for non-adherence which does not rely
  on the same `unconfoundedness' assumption and is less vulnerable to posit
 ivity violations (e.g.\, it can give valid results even under conditions w
 here non-adherence is guaranteed). Unlike many previous Instrumental Varia
 ble approaches\, it makes full use of the repeatedly measured outcome data
 \, and allows for a time-varying effect of treatment adherence on a partic
 ipant's weight. We show that it provides a natural vehicle for defining tw
 o distinct hypothetical estimands: the treatment effect if all participant
 s would have adhered to semaglutide\, and the treatment effect if all part
 icipants would have adhered to both semaglutide and placebo. When applied 
 to the STEP 1 study\, they both suggest a sustained\, slowly decaying weig
 ht loss effect of semaglutide treatment.\n\nSpeaker Bio\n\nPlease visit: h
 ttps://experts.exeter.ac.uk/34216-jack-bowden.\n
DTSTART:20241120T203000Z
DTEND:20241120T213000Z
SUMMARY:Instrumental Variable methods to target Hypothetical Estimands with
  longitudinal repeated measures data: Application to the STEP 1 trial
URL:/epi-biostat-occh/channels/event/instrumental-vari
 able-methods-target-hypothetical-estimands-longitudinal-repeated-measures-
 data-360433
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