Robust estimation of constrained covariance matrices for confirmatory factor analysis

Confirmatory factor analysis (CFA) is a data analysis procedure that is widely used in social and behavioral sciences in general and other applied sciences that deal with large quantities of data (variables). The classical estimator (and inference) procedures are based either on the maximum likelihood (ML) or generalized least squares (GLS) approaches which are known to be nonrobust to departures from the multivariate normal assumption underlying CFA. A natural robust estimator is obtained by first estimating the (mean and) covariance matrix of the manifest variables and then "plug-in" this statistic into the ML or GLS estimating equations. This two-stage method however does not fully take into account the covariance structure implied by the CFA model. An S-estimator for the parameters of the CFA model that is computed directly from the data is proposed instead and the corresponding estimating equations and an iterative procedure are derived. It is also shown that the two estimators have different asymptotic properties. A simulation study compares the finite sample properties of both estimators showing that the proposed direct estimator is more stable (smaller MSE) than the two-stage estimator.

Simulation Based Estimation for Generalized Latent Linear Variables Models

Generalized Linear Latent Variables Models (GLLVM) constitute a broad class of models that offer a general framework for modeling relationships between manifest and latent variables, as the manifest variables can follow any distribution of the exponential family (e.g, binomial, multinomial or normal). However, the estimation of such models is quite difficult due to the complexity of the associated log-likelihood function which contains integrals without closed form expression, except in the normal case. We propose a method based on indirect inference (Gourieroux, Monfort, and Renault 1993) which starts from an easy to compute estimator that is then corrected for bias

Comparison of dual-mobility cup and unipolar cup for prevention of dislocation after revision total hip arthroplasty.

Background and purpose Revision total hip arthroplasty (THA) is associated with higher dislocation rates than primary THA. We compared the risk of dislocation within 6 months and all-cause re-revision during the whole study period using either the dual-mobility cup or the unipolar cup. Methods We used a prospective hospital registry-based cohort including all total and cup-only revision THAs performed between 2003 and 2013. The cups used were either dual-mobility or unipolar; the choice was made according to the preference of the surgeon. 316 revision THAs were included. The mean age of the cohort was 69 (25–98) years and 160 THAs (51%) were performed in women. The dual-mobility group (group 1) included 150 THAs (48%) and the mean length of follow-up was 31 (0–128) months. The unipolar group (group 2) included 166 THAs (53%) and the mean length of follow-up was 52 (0–136) months. Results The incidence of dislocation within 6 months was significantly lower with the dual-mobility cup than with the unipolar cup (2.7% vs. 7.8%). The unadjusted risk ratio (RR) was 0.34 (95% CI: 0.11–1.02) and the adjusted RR was 0.28 (95% CI: 0.09–0.87). The number of patients needed to treat with a dualmobility cup in order to prevent 1 case of dislocation was 19. The unadjusted incidence rate ratio for all-cause re-revision in the dual-mobility group compared to the unipolar group was 0.6 (95% CI: 0.3–1.4). Interpretation Use of a dual-mobility rather than a unipolar cup in revision THA reduced the risk of dislocation within 6 months.</p

Reply to Sorooshian and Snow, "Is Alternate-Day Therapeutic Drug Monitoring in the Intensive Care Unit Not Intensive Enough?"

Commentaire au sujet de FOURNIER, Anne et al. Impact of Real-Time Therapeutic Drug Monitoring on the Prescription of Antibiotics in Burn Patients Requiring Admission to the Intensive Care Unit. In: Antimicrobial Agents and Chemotherapy, 2018, vol. 62, n° 3. doi: 10.1128/AAC.01818-17 https://archive-ouverte.unige.ch/unige:12789

Agreement between spirometers: a challenge in the follow-up of patients and populations?

BACKGROUND: Long-term cohort studies and lung function laboratories are confronted with the need for replacement of spirometers. Lack of agreement between spirometers might affect the longitudinal comparison of data, notably when replacing conventional by portable spirometers. OBJECTIVES: To compare the handheld EasyOne (EO) with the conventional SensorMedics (SM) spirometer, and to analyze the interdevice reproducibility of EO spirometers. METHODS: In total, 82 volunteers completed spirometry sessions with 1 SM and 2 of 3 EO spirometers following a Latin square design. Analyses of differences in forced vital capacity (FVC), forced expiratory flow in 1 s (FEV1), FEV1/FVC and mean forced expiratory flow calculated between 25 and 75% of the FVC between spirometers used a mixed effect model with a random intercept for each subject and the effect of the device as fixed effect adjusted for sex, age, height and order of spirometer tested. Bland-Altman plots show the 95% limits of agreement. RESULTS: Comparisons between EO and SM showed relatively small mean differences of <3%, but systematically lower values for FVC and FEV1 in all EO devices. The 95% agreement exceeded the limits for FEV1 by 50 ml in 2 EO spirometers. The EO interdevice comparisons showed mean differences and limits of agreement within established thresholds, thus indicating fair accuracy when comparing devices. Repeats with the same spirometer did not result in statistically significant differences. CONCLUSIONS: This study suggests fair agreement between the handheld and the conventional spirometer. Differences slightly exceeding limits for FEV1 in 2 EO devices might be considered mostly irrelevant for clinical practice. However, the systematically lower FVC and FEV1 observed with EO may be significant for epidemiological studies, thus justifying inspection before replacing devices

Staphylococcus aureus carriage at admission predicts early-onset pneumonia after burn trauma.

Early-onset pneumonia (EOP) is frequent after burn trauma, increasing morbidity in the critical resuscitation phase, which may preclude early aggressive management of burn wounds. Currently, however, preemptive treatment is not recommended. The aim of this study was to identify predictive factors for EOP that may justify early empirical antibiotic treatment. Data for all burn patients requiring ≥4 h mechanical ventilation (MV) who were admitted between January 2001 and October 2012 were extracted from the hospital's computerized information system. We reviewed EOP episodes (≤7 days) among patients who underwent endotracheal aspiration (ETA) within 5 days after admission. Univariate and multivariate analyses were performed to identify independent factors associated with EOP. Logistic regression was used to identify factors predicting EOP development. During the study period, 396 burn patients were admitted. ETA was performed within 5 days in 204/290 patients receiving ≥4 h MV. One hundred and eight patients developed EOP; 47 cases were caused by Staphylococcus aureus, 37 by Haemophilus influenzae, and 23 by Streptococcus pneumoniae. Among the 33 patients showing S. aureus positivity on ETA samples, 16 (48.5 %) developed S. aureus EOP. Among the 156 S. aureus non-carriers, 16 (10.2 %) developed EOP. Staphylococcus aureus carriage independently predicted EOP (p &lt; 0.0001). We identified S. aureus carriage as an independent and strong predictor of EOP. As rapid point-of-care testing for S. aureus is readily available, we recommend testing of all patients at admission for burn trauma and the consideration of early preemptive treatment in all positive patients. Further studies are needed to evaluate this new strategy

Prognostication of Mortality in Critically Ill Patients With Severe Infections.

BACKGROUND: The purpose of this study was to confirm the prognostic value of pancreatic stone protein (PSP) in patients with severe infections requiring ICU management and to develop and validate a model to enhance mortality prediction by combining severity scores with biomarkers. METHODS: We enrolled prospectively patients with severe sepsis or septic shock in mixed tertiary ICUs in Switzerland (derivation cohort) and Brazil (validation cohort). Severity scores (APACHE [Acute Physiology and Chronic Health Evaluation] II or Simplified Acute Physiology Score [SAPS] II) were combined with biomarkers obtained at the time of diagnosis of sepsis, including C-reactive-protein, procalcitonin (PCT), and PSP. Logistic regression models with the lowest prediction errors were selected to predict in-hospital mortality. RESULTS: Mortality rates of patients with septic shock enrolled in the derivation cohort (103 out of 158) and the validation cohort (53 out of 91) were 37% and 57%, respectively. APACHE II and PSP were significantly higher in dying patients. In the derivation cohort, the models combining either APACHE II, PCT, and PSP (area under the receiver operating characteristic curve [AUC], 0.721; 95% CI, 0.632-0.812) or SAPS II, PCT, and PSP (AUC, 0.710; 95% CI, 0.617-0.802) performed better than each individual biomarker (AUC PCT, 0.534; 95% CI, 0.433-0.636; AUC PSP, 0.665; 95% CI, 0.572-0.758) or severity score (AUC APACHE II, 0.638; 95% CI, 0.543-0.733; AUC SAPS II, 0.598; 95% CI, 0.499-0.698). These models were externally confirmed in the independent validation cohort. CONCLUSIONS: We confirmed the prognostic value of PSP in patients with severe sepsis and septic shock requiring ICU management. A model combining severity scores with PCT and PSP improves mortality prediction in these patients

Antibiotic consumption to detect epidemics of Pseudomonas aeruginosa in a burn centre: A paradigm shift in the epidemiological surveillance of Pseudomonas aeruginosa nosocomial infections.

The control of antibiotic resistance and nosocomial infections are major challenges for specialized burn centres. Early detection of those epidemic outbreaks is crucial to limit the human and financial burden. We hypothesize that data collected by antibiotic consumption medico-economic surveys could be used as warning signal to detect early nosocomial outbreaks. A retrospective analysis was conducted that included all burn patients staying &gt;48h on the Lausanne BICU (Burn Intensive Care Unit) between January 2001 and October 2012 who received systemic therapeutic antibiotics. Infection episodes were characterized according to predefined criteria. Antibiotic consumption data, obtained from the quarterly surveillance of drug consumption surveys, were translated into defined daily doses (DDDs). In total, 297 out of 414 burn patients stayed &gt;48h, giving a total of 7458 'burn-days'. We identified 610 infection episodes (burn wound [32.0%], respiratory [31.1%], and catheter [21.8%]), from 774 microorganisms. Pseudomonas aeruginosa (26.2%), Staphylococcus aureus (11.5%), and Candida albicans (7.0%) were the main pathogens. We observed three distinct outbreaks of P. aeruginosa infections in 2002-2003, 2006, and 2009-2011. These outbreaks correlated with an increase in the DDDs of anti-Pseudomonas antibiotics. Our data support a paradigm shift in the epidemiological surveillance of nosocomial P. aeruginosa epidemics in burn centres, using the rise in antibiotic consumption as an early trigger to initiate the molecular typing of P. aeruginosa strains and the reinforcement of standard infection control procedures