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Background Intention-to-treat (ITT) analysis requires all randomised individuals to be included in the analysis in the groups to which they were randomised. However, there is confusion about how ITT analysis should be performed in the presence of missing outcome data. Purposes To explain, justify, and illustrate an ITT analysis strategy for randomised trials with incomplete outcome data. Methods We consider several methods of analysis and compare their underlying assumptions, plausibility, and numbers of individuals included. We illustrate the ITT analysis strategy using data from the UK700 trial in the management of severe mental illness. Results Depending on the assumptions made about the missing data, some methods of analysis that include all randomised individuals may be less valid than methods that do not include all randomised individuals. Furthermore, some methods of analysis that include all randomised individuals are essentially equivalent to methods that do not include all randomised individuals. Limitations This work assumes that the aim of analysis is to obtain an accurate estimate of the difference in outcome between randomised groups and not to obtain a conservative estimate with bias against the experimental intervention. Conclusions Clinical trials should employ an ITT analysis strategy, comprising a design that attempts to follow up all randomised individuals, a main analysis that is valid under a stated plausible assumption about the missing data, and sensitivity analyses that include all randomised individuals in order to explore the impact of departures from the assumption underlying the main analysis. Following this strategy recognises the extra uncertainty arising from missing outcomes and increases the incentive for researchers to minimise the extent of missing data.

Authors of randomized trial reports seem to hold a variety of views regarding the relationship between missing outcome data (MOD) and intention to treat (ITT). The objectives of this study were to systematically investigate how authors of methodology articles define ITT in the presence of MOD, how they recommend handling MOD under ITT, and to make a proposal for potential improvement in the definition and use of ITT in relation to MOD. We systematically searched MEDLINE in February 2009 for methodological articles written in English that devoted at least one paragraph to ITT and two other paragraphs to either ITT or MOD. We excluded original trial reports, observational studies, and clinical systematic reviews. Working in teams of two, we independently extracted relevant information from each eligible article. Of 1007 titles and abstracts reviewed, 66 articles met eligibility criteria. Five (8%) did not provide a definition of ITT; 25 (38%) mentioned MOD but did not discuss its relationship to ITT; and 36 (55%) discussed the relationship of MOD with ITT. These 36 articles described one or more of three statements: complete follow-up is required for ITT (58%); ITT and MOD are separate issues (17%); and ITT requires a specific strategy for handling MOD (78%); 17 (47%) endorsed more than one relationship. The most frequently mentioned strategies for handling MOD within ITT were: using the last outcome carried forward (50%); sensitivity analysis (50%); and use of available data to impute missing data (46%). We found that there is no consensus on the definition of ITT in relation to MOD. For conceptual clarity, we suggest that both reports of randomized trials and systematic reviews separately consider and describe how they deal with participants with complete data and those with MOD.

Treatment switching, also called crossover, is common in clinical trials because of ethical concerns or other reasons. When it occurs and the primary objective is to identify treatment effects, the most widely used intention-to-treat analysis may lead to underpowered trials. Here, we presented an approach to preview power reductions and to estimate sample sizes required to achieve the desired power when treatment switching occurs in the intention-to-treat analysis. We proposed a simulation-based approach and developed an R package to perform power and sample sizes estimation in clinical trials with treatment switching. We simulated a number of randomized trials incorporating treatment switching and investigated the impact of the relative effectiveness of the experimental treatment to the control, the switching probability, the switching time, and the deviation between the assumed and the real distributions for the survival time on power reductions and sample sizes estimation. The switching probability and the switching time are key determinants for significant power decreasing and thus sample sizes surging to maintain the desired power. The sample sizes required in randomized trials absence of treatment switching vary from around four-fifths to one-seventh of the sample sizes required in randomized trials allowing treatment switching as the switching probability increases. The power reductions and sample sizes increase with the decrease of switching time. The simulation-based approach not only provides a preview for power declining but also calculates the required sample size to achieve an expected power in the intention-to-treat analysis when treatment switching occurs. It will provide researchers and clinicians with useful information before randomized controlled trials are conducted.

IntroductionThe minimal stroke severity justifying endovascular intervention remains elusive; however, a significant proportion of patients presenting with large vessel occlusion (LVO) and mild symptoms subsequently decline and face poor outcomes.ObjectiveTo evaluate our experience with these patients by comparing best medical therapy with thrombectomy in an intention-to-treat analysis.MethodsAnalysis of prospectively collected data of all consecutive patients with National Institutes of Health Stroke Scale (NIHSS) score ≤5, LVO on CT angiography, and baseline modified Rankin Scale (mRS) score 0–2 from November 2014 to May 2016. After careful discussion with patients/family, a decision to pursue medical or interventional therapy was made. Deterioration (development of aphasia, neglect, and/or significant weakness) triggered reconsideration of thrombectomy. The primary outcome measure was NIHSS shift (discharge NIHSS score minus admission NIHSS score).ResultsOf the 32 patients qualifying for the study, 22 (69%) were primarily treated with medical therapy and 10 (31%) intervention. Baseline characteristics were comparable. Nine (41%) medically treated patients had subsequent deterioration requiring thrombectomy. Median time from arrival to deterioration was 5.2 hours (2.0–25.0). Successful reperfusion (modified Treatment in Cerebral Infarction 2b−3) was achieved in all 19 thrombectomy patients. The NIHSS shift significantly favored thrombectomy (−2.5 vs 0; p<0.01). The median NIHSS score at discharge was low with both thrombectomy (1 (0–3)) and medical therapy (2 (0.5–4.5)). 90-Day mRS 0–2 rates were 100% and 77%, respectively (p=0.15). Multivariable linear regression indicated that thrombectomy was independently associated with a beneficial NIHSS shift (unstandardized β −4.2 (95% CI −8.2 to −0.1); p=0.04).ConclusionsThrombectomy led to a shift towards a lower NIHSS in patients with LVO presenting with minimal stroke symptoms. Despite the overall perception that this condition is benign, nearly a quarter of patients primarily treated with medical therapy did not achieve independence at 90 days.

Adoption of the estimands framework by regulatory authorities and the pharmaceutical industry is expected to lead to global changes in trial design, trial conduct, and interpretation of results. The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) released “Estimands and sensitivity analyses”, as an addendum to their ICH E9 guideline “Statistical Principles for Clinical Trials” [1]. [...]if an intention-to-treat analysis is targeted, events after randomization may preclude observation of the outcomes (e.g., death) or complicate their interpretation (e.g., use of rescue medication).

Abstract Objective To investigate whether analysis of the modified intention-to-treat (mITT) population with postrandomization exclusion of patients from analysis is associated with biased estimates of treatment effect compared to the conservative intention-to-treat (ITT) population. Study Design and Setting Placebo-controlled, blinded randomized trials on biological or targeted interventions for rheumatoid arthritis were identified through a systematic search. Two authors independently extracted data. A random-effects meta-analysis was used to combine odds ratios as an expression of treatment effect and stratify according to the different analysis populations. Results Seventy-two randomized trials were included and analyzed (23,842 patients). Thirty trials analyzed the ITT population, 37 analyzed an mITT population, and 5 trials had an unclear analysis population. The treatment effect of active intervention compared to control, when based on mITT, was comparable to ITT (odds ratio 3.76 [95% confidence interval 3.09, 4.57], and 3.47 [2.77, 4.34]; comparison P  = 0.60). Conclusion We found no difference in the treatment effect between randomized trials using ITT and mITT analyses populations. This suggests that the mITT approach in rheumatoid arthritis trials investigating biological or targeted interventions does not introduce bias compared to ITT.

Abstract Objectives In randomized trials, the primary analysis should be consistent with the intention-to-treat (ITT) principle and should address missing data appropriately to draw valid inferences. This review focuses on current practices relating to the ITT principle and methods to handle missing data in the major musculoskeletal journals. Study Design and Setting A systematic review of randomized trials published in 2010 and 2011 in five musculoskeletal journals was performed. Results We reviewed 91 trials: 38% performed a full ITT analysis (analyzing outcome data for all randomized participants) and 31% performed a partial ITT analysis (excluding participants with no follow-up data). The overall median dropout was 12%; 60% of trials had more than 10% dropouts, and 32% of trials had more than 20% dropouts. Among those that performed an ITT analysis, the majority adopted a form of single imputation; last observation carried forward was the designated approach in most cases. Mixed models for repeated measures and/or multiple imputations were limited to eight trials. Conclusion It appears that many trials reporting missing data are inappropriately analyzed and may therefore be prone to biased estimates and invalid inferences.

Introduction Cerebral small vessel disease (SVD) is an important cause of dementia that lacks effective treatment. We evaluated the efficacy and safety of cilostazol, an antiplatelet agent with potential neurovascular protective effects, in slowing the progression of white matter hyperintensities (WMHs) in stroke‐ and dementia‐free subjects harboring confluent WMH on magnetic resonance imaging (MRI). Methods In this single‐center, randomized, double‐blind, placebo‐controlled study, we randomized stroke‐ and dementia‐free subjects with confluent WMHs to receive cilostazol or placebo for 2 years in a 1:1 ratio. The primary outcome was change in WMH volume over 2 years. Secondary outcomes were changes in brain volumes, lacunes, cerebral microbleeds, perivascular space, and alterations in white matter microstructural integrity, cognition, motor function, and mood. Results We recruited 120 subjects from October 27, 2014, to January 21, 2019. A total of 55 subjects in the cilostazol group and 54 subjects in the control group were included for intention‐to‐treat analysis. At 2‐year follow‐up, the changes in WMH volume were not statistically different between cilostazol treatment and placebo (0.3±1.0 mL vs −0.1±0.8 mL, p = 0.167). Secondary outcomes, bleeding and vascular events, were also not statistically different between the two groups. Discussion In this trial with stroke‐ and dementia‐free subjects with confluent WMHs, cilostazol did not impact WMH progression but demonstrated an acceptable safety profile. Future studies should address the treatment effects of cilostazol on subjects at different clinical stages of SVD.

In this ongoing, randomized, phase 3 trial, sotrovimab (a SARS-CoV-2–targeted monoclonal antibody) or placebo was administered to outpatients within 5 days after the onset of Covid-19 symptoms. The incidence of hospitalization for any cause or death was lower among patients who received sotrovimab (1% vs. 7%).

Patients with chronic coronary disease were randomly assigned to receive 0.5 mg of colchicine once daily or matching placebo. The incidence of the composite end point of cardiovascular death, spontaneous myocardial infarction, ischemic stroke, or ischemia-driven coronary revascularization was significantly lower with colchicine than with placebo.