Evaluation of a weighting approach for performing sensitivity analysis after multiple imputation

Abstract Background Multiple imputation (MI) is a well-recognised statistical technique for handling missing data. As usually implemented in standard statistical software, MI assumes that data are ‘Missing at random’ (MAR); an assumption that in many settings is implausible. It is not possible to distinguish whether data are MAR or ‘Missing not at random’ (MNAR) using the observed data, so it is desirable to discover the impact of departures from the MAR assumption on the MI results by conducting sensitivity analyses. A weighting approach based on a selection model has been proposed for performing MNAR analyses to assess the robustness of results obtained under standard MI to departures from MAR. Methods In this article, we use simulation to evaluate the weighting approach as a method for exploring possible departures from MAR, with missingness in a single variable, where the parameters of interest are the marginal mean (and probability) of a partially observed outcome variable and a measure of association between the outcome and a fully observed exposure. The simulation studies compare the weighting-based MNAR estimates for various numbers of imputations in small and large samples, for moderate to large magnitudes of departure from MAR, where the degree of departure from MAR was assumed known. Further, we evaluated a proposed graphical method, which uses the dataset with missing data, for obtaining a plausible range of values for the parameter that quantifies the magnitude of departure from MAR. Results Our simulation studies confirm that the weighting approach outperformed the MAR approach, but it still suffered from bias. In particular, our findings demonstrate that the weighting approach provides biased parameter estimates, even when a large number of imputations is performed. In the examples presented, the graphical approach for selecting a range of values for the possible departures from MAR did not capture the true parameter value of departure used in generating the data. Conclusions Overall, the weighting approach is not recommended for sensitivity analyses following MI, and further research is required to develop more appropriate methods to perform such sensitivity analyses

The impact of missing data on analyses of a time-dependent exposure in a longitudinal cohort: A simulation study

Background: Missing data often cause problems in longitudinal cohort studies with repeated follow-up waves. Research in this area has focussed on analyses with missing data in repeated measures of the outcome, from which participants with missing exposure data are typically excluded. We performed a simulation study to compare complete-case analysis with Multiple imputation (MI) for dealing with missing data in an analysis of the association of waist circumference, measured at two waves, and the risk of colorectal cancer (a completely observed outcome). Methods. We generated 1,000 datasets of 41,476 individuals with values of waist circumference at waves 1 and 2 and times to the events of colorectal cancer and death to resemble the distributions of the data from the Melbourne Collaborative Cohort Study. Three proportions of missing data (15, 30 and 50%) were imposed on waist circumference at wave 2 using three missing data mechanisms: Missing Completely at Random (MCAR), and a realistic and a more extreme covariate-dependent Missing at Random (MAR) scenarios. We assessed the impact of missing data on two epidemiological analyses: 1) the association between change in waist circumference between waves 1 and 2 and the risk of colorectal cancer, adjusted for waist circumference at wave 1; and 2) the association between waist circumference at wave 2 and the risk of colorectal cancer, not adjusted for waist circumference at wave 1. Results: We observed very little bias for complete-case analysis or MI under all missing data scenarios, and the resulting coverage of interval estimates was near the nominal 95% level. MI showed gains in precision when waist circumference was included as a strong auxiliary variable in the imputation model. Conclusions: This simulation study, based on data from a longitudinal cohort study, demonstrates that there is little gain in performing MI compared to a complete-case analysis in the presence of up to 50% missing data for the exposure of interest when the data are MCAR, or missing dependent on covariates. MI will result in some gain in precision if a strong auxiliary variable that is not in the analysis model is included in the imputation model. © 2013 Karahalios et al.; licensee BioMed Central Ltd

Comparison of Intraoperative Indocyanine Green Videoangiography vs Postoperative Catheter Angiography to Confirm Microsurgical Occlusion of Spinal Dorsal Intradural Arteriovenous Fistulas

BACKGROUND: Dorsal intradural arteriovenous fistulas (DI-AVFs) represent 80% of spinal AVFs. Microsurgical clip occlusion is a durable treatment that uses preoperative and postoperative digital subtraction angiography (DSA) as standard practice. Intraoperative indocyanine green videoangiography (ICG-VA) is a valuable intraoperative adjunct in these cases. Intraoperative ICG-VA findings have not been compared with postoperative DSA findings. OBJECTIVE: To assess the diagnostic value of intraoperative ICG-VA vs postoperative DSA for spinal DI-AVFs. METHODS: A multi-institutional database of vascular malformations was queried for all surgically managed cases of DI-AVF. Patients with both intraoperative ICG-VA and postoperative DSA were included. Demographic and radiologic data, intraoperative findings, and surgical outcomes data were retrospectively analyzed. RESULTS: Forty-five patients with DI-AVF were identified (male sex, 32; mean age, 61.9 [range, 26-85] years). All DI-AVFs were treated with interruption of the fistula with clip occlusion of the draining vein. Intraoperative ICG-VA showed complete obliteration in all patients. Postoperative DSA was performed for 40 patients and confirmed complete obliteration in all patients. The negative predictive value of ICG-VA confirming complete occlusion of the DI-AVFs was 100%. Eighteen patients (47%) experienced clinical improvement, and 16 (42%) experienced no change in condition. CONCLUSION: ICG-VA is useful for intraoperative identification of DI-AVFs and confirmation of complete microsurgical occlusion. Correlation between intraoperative ICG-VA and postoperative DSA findings demonstrates the diagnostic power of ICG-VA. This finding suggests that postoperative DSA is unnecessary when intraoperative ICG-VA confirms complete occlusion of the DI-AVF, which will spare patients the procedural risk and cost of this invasive procedure

Cost Comparison of Microsurgery vs Endovascular Treatment for Ruptured Intracranial Aneurysms: A Propensity-Adjusted Analysis

BACKGROUND: In specialized neurosurgical centers, open microsurgery is routinely performed for aneurysmal subarachnoid hemorrhage (aSAH). OBJECTIVE: To compare the cost of endovascular vs microsurgical treatment for aSAH at a single quaternary center. METHODS: All patients undergoing aSAH treatment from July 1, 2014, to July 31, 2019, were retrospectively reviewed. Patients were grouped based on primary treatment (microsurgery vs endovascular treatment). The primary outcome was the difference in total cost (including hospital, discharge facility, and all follow-up) using a propensity-adjusted analysis. RESULTS: Of 384 patients treated for an aSAH, 234 (61%) were microsurgically treated and 150 (39%) were endovascularly treated. The mean cost of index hospitalization for these patients was marginally higher ($9504) for endovascularly treated patients ($103 980) than for microsurgically treated patients ($94 476) ( P = .047). For the subset of patients with follow-up data available, the mean total cost was$45 040 higher for endovascularly treated patients ($159 406, n = 59) than that for microsurgically treated patients ($114 366, n = 105) ( P \u3c .001). After propensity scoring (adjusted for age, sex, comorbidities, Glasgow Coma Scale score, Hunt and Hess grade, Fisher grade, aneurysms, and type/size/location), linear regression analysis of patients with follow-up data available revealed that microsurgery was independently associated with healthcare costs that were $37 244 less than endovascular treatment costs ( P \u3c .001). An itemized cost analysis suggested that this discrepancy was due to differences in the rates of aneurysm retreatment and long-term surveillance. CONCLUSION: Microsurgical treatment for aSAH is associated with lower total healthcare costs than endovascular therapy. Aneurysm surveillance after endovascular treatments, retreatment, and device costs warrants attention in future studies

Chronic headaches and middle meningeal artery embolization

BACKGROUND: The middle meningeal artery (MMA) has been implicated in chronic headaches, but no studies have examined the relationship between MMA embolization and headaches. METHODS: Patients treated with MMA embolization for a chronic subdural hematoma (cSDH) between January 1, 2018, and December 31, 2020, were retrospectively assessed. Patients with a Glasgow Coma Scale (GCS) score of 15 at discharge received a follow-up telephone call to assess their history of chronic headache, defined as a headache ≥2 years before the cSDH and symptoms ≥2 days/month. A Headache Impact Test (HIT-6) was performed during the follow-up telephone call. The primary outcome was resolution or improvement of headaches after embolization. RESULTS: Of 76 patients undergoing MMA embolization for a cSDH during the study period, 56 (74%) had a discharge GCS score of 15. Of these 56 patients, 46 (82%) responded to a follow-up telephone call and were analyzed (mean [SD] age 68 [11] years; 36 [78%] men and 10 [22%] women). Nine (20%) reported chronic headaches before embolization. With a mean (SD) follow-up of 489 (173) days, eight of the nine patients reported improvement of chronic headaches, with seven having complete resolution. For these nine patients, the mean (SD) HIT-6 score was significantly higher before embolization than after embolization (64 [7.1] vs 40 [9.1], p\u3c0.001). CONCLUSION: In patients with chronic headaches who underwent MMA embolization for a cSDH, the majority reported improvement of headaches after the procedure. Future prospective studies are warranted to assess the usefulness of MMA embolization to treat chronic headaches

Endovascular treatment of ruptured anterior communicating aneurysms: a 17-year institutional experience with coil embolization

BACKGROUND: Ruptured anterior communicating artery (ACoA) aneurysms can be challenging to treat via an endovascular procedure. This study analyzed retreatment rates and neurological outcomes associated with ruptured ACoA aneurysms treated via endovascular coiling. METHODS: All patients with a ruptured ACoA aneurysm treated with endovascular coiling from 2003 to 2019 were retrospectively analyzed at a single center. Two comparisons were performed: no retreatment versus retreatment and coil embolization versus balloon-assisted coil embolization. Outcomes included retreatment and neurological outcome assessed via modified Rankin Scale (mRS). RESULTS: During the study period, 186 patients with ruptured ACoA aneurysms underwent coil embolization. Treatment included standard coil embolization (68.3%, n=127), balloon-assisted coiling (28.5%, n=53), and stent-assisted embolization (2.7%, n=5). Angiographic outcomes were as follows: class I, 65.1% (n=121); class II, 28.5% (n=53); and class III, 6.5% (n=12). There were no aneurysm reruptures after the index procedure. The mean (SD) mRS score was 2.7 (2.0) at last follow-up (mortality, 19 (10%)). Retreatment occurred in 9.7% (n=18). Patients with retreatment were younger with lower-grade subarachnoid hemorrhage and more favorable functional status at discharge. Patients with aneurysms \u3e7 mm (n=36) were significantly more likely to have recurrence (22.2% vs 6.7%, P=0.005). CONCLUSIONS: Endovascular treatment of ruptured ACoA aneurysms is safe and is associated with low mortality and retreatment rates. Younger patients with favorable functional status and larger aneurysm size are more likely to be retreated. Ruptured aneurysms \u3c4 mm, although prevalent in the study (29%), never required retreatment