Patient Outcomes After Delirium Screening and Incident Alzheimer's Disease or Related Dementias in Skilled Nursing Facilities.

BACKGROUND: The extent to which a positive delirium screening and new diagnosis of Alzheimer's disease or related dementias (ADRD) increases the risk for re-hospitalization, long-term nursing home placement, and death remains unknown. OBJECTIVE: To compare long-term outcomes among newly admitted skilled nursing facility (SNF) patients with delirium, incident ADRD, and both conditions. DESIGN, SETTING, AND PARTICIPANTS: A retrospective cohort study of Medicare beneficiaries who entered a SNF from hospital with a minimum 14-day stay (n = 100,832) from 2015 to 2016. MAIN MEASURES: Return to home, hospital readmission, admission to a long-term care facility, or death. KEY RESULTS: Patients with delirium were as likely to be discharged home as patients diagnosed with ADRD (HR: 0.63, 95% CI: 0.59, 0.67; HR: 0.65, 95% CI: 0.64, 0.67). Patients with both delirium and ADRD were less likely to be discharged home (HR: 0.49, 95% CI: 0.47, 0.52) and showed increased risk of death (HR: 1.30, 95% CI: 1.17, 1.45). Patients with ADRD, regardless of delirium screening status, had increased risk for long-term nursing home care transfer (HR: 1.66, 95% CI: 1.63, 1.70; HR: 1.76, 95% CI: 1.69, 1.82). Patients with delirium and no ADRD showed increased risk of transfer to long-term nursing home care (HR: 1.25, 95% CI: 1.18, 1.33). The rate of deaths was higher among patients who screened positive for delirium without ADRD compared to the no delirium and no ADRD groups (HR: 2.35, 95% CI: 2.11, 2.61). CONCLUSION: A positive delirium screening increased risk of death and transfer to long-term care in the first 100 days after admission regardless of incident ADRD diagnosis. Patients with delirium and/or ADRD also are less likely to be discharged home. Our study builds on the evidence base that delirium is important to address in older adults as it is associated with negative outcomes.

Structure-Kinetics Relationships of Opioids from Metadynamics and Machine Learning Analysis.

The nation's opioid overdose deaths reached an all-time high in 2021. The majority of deaths are due to synthetic opioids represented by fentanyl. Naloxone, which is a FDA-approved reversal agent, antagonizes opioids through competitive binding at the µ-opioid receptor (mOR). Thus, knowledge of the opioid's residence time is important for assessing the effectiveness of naloxone. Here, we estimated the residence times (τ) of 15 fentanyl and 4 morphine analogs using metadynamics and compared them with the most recent measurement of the opioid kinetic, dissociation, and naloxone inhibitory constants (Mann et al. Clin. Pharmacol. Therapeut. 2022, 120, 1020-1232). Importantly, the microscopic simulations offered a glimpse at the common binding mechanism and molecular determinants of dissociation kinetics for fentanyl analogs. The insights inspired us to develop a machine learning approach to analyze the kinetic impact of fentanyl's substituents based on the interactions with mOR residues. This proof-of-concept approach is general; for example, it may be used to tune ligand residence times in computer-aided drug discovery.

Tracing-corrected estimates of disengagement from HIV care and mortality among patients enrolling in HIV care without overt immunosuppression in Tanzania.

In the era of "test and treat", it is important to understand HIV care outcomes and their determinants in patients presenting to care with early-stage disease. We surveyed 924 adults newly enrolling in HIV care at four clinics in Tanzania before the adoption of universal treatment eligibility, and collected longitudinal clinical data. Participants who defaulted from care were tracked in the community. Cumulative incidence of disengagement from care and death was estimated using competing risk methods. By 12 months after enrollment, 18.2% of patients had disengaged from care and 6.9% had died. Factors associated with disengagement included male sex (adjusted subhazard ratio [aSHR] versus female = 1.75, 95% confidence interval [CI]: 1.06-2.89), provider-initiated HIV diagnosis (aSHR versus self-referred = 1.71, 95% CI: 1.03-2.86), ineligibility for antiretroviral treatment (ART) at enrollment (aSHR versus eligibility = 2.82, 95% CI: 1.84-4.32) and increased anticipated stigma score (aSHR = 1.04 per 5-point increase, 95% CI: 1.02-1.05). Higher life satisfaction score (aSHR = 0.97 per 5-point increase, 95% CI: 0.95-0.99) and having 1-2 close friends (aSHR versus none = 0.58, 95% CI: 0.47-0.71) were protective. The findings highlight the continued importance of social environment for HIV care outcomes and the potential of universal ART eligibility to reduce HIV care attrition.

Linking Epidemiology and Whole-Genome Sequencing to Investigate Salmonella Outbreak, Massachusetts, USA, 2018.

Cross-discipline collaboration among state and local health departments improved foodborne illness surveillance for a 2018 Salmonella enterica serovar Enteritidis outbreak in Massachusetts, USA. Prompt linking of epidemiologic and laboratory data and implementation of in-state whole-genome sequencing and analysis improved public health surveillance capacity for outbreak detection and control.

Gender Differences and Psychosocial Factors Associated with Quality of Life Among ART Initiators in Oromia, Ethiopia.

Health-related quality of life (HRQoL) is an important outcome to assess among persons living with HIV/AIDS, but few studies have been conducted in sub-Saharan Africa. We examined HRQoL among 1180 ART-initiating adults from six clinics in Ethiopia in 2012-2013, and compared the correlates of two subscale scores between women and men. Women scored significantly higher than men on both overall function (8.4 points higher) and life satisfaction (6.3 points higher). In multivariable models, psychological distress, low CD4+ count, unemployment, and food insecurity were associated with lower quality of life scores among women and men. Men whose last sexual encounter occurred 3 months to 1 year from the interview date had lower overall function and life satisfaction scores. Men between the ages of 30-39 had lower overall function scores. Protestant women and women in the low-middle social support category had lower life satisfaction scores. Assessment of HRQoL over time will help inform HIV care and treatment practices to ensure favorable patient outcomes.

Efficacy and safety of argatroban and bivalirudine in patients with suspected heparin-induced thrombocytopenia.

BACKGROUND: Argatroban is the only commercially available Food and Drug Administration (FDA)-approved anticoagulant for managing heparin-induced thrombocytopenia (HIT). However, bivalirudin may be an attractive alternative. OBJECTIVE: To assess the efficacy and safety of argatroban and bivalirudin in patients with suspected HIT. METHODS: This single-center, retrospective analysis included patients who received argatroban or bivalirudin for at least 24 hours between January 1, 2000, and June 30, 2012. The primary end point assessed anticoagulation goals, specifically time to therapeutic activated partial thromboplastin time (aPTT) goal and percentage of aPTT values within therapeutic range. Secondary end points included new thromboembolic events, bleeding, and mortality. RESULTS: Of the 68 patients who met the inclusion criteria, 48 received argatroban and 20 received bivalirudin. Baseline characteristics were similar between the 2 groups except for age, percentage of patients with liver dysfunction, aPTT immediately prior to drug initiation, and the serotonin release assay results. The mean ± SD times to reach therapeutic aPTT goal for argatroban and bivalirudin were 14 ± 15 and 7 ± 8 hours, respectively (P = 0.024). The mean ± SD percentage of aPTT values within therapeutic aPTT goal was 69% ± 23% for argatroban and 84% ± 18% for bivalirudin (P = 0.005). Rates of thromboembolic events were similar between the 2 groups, as were the rates of bleeding and all-cause mortality. CONCLUSIONS: Bivalirudin appears to reach therapeutic aPTT goal faster with more aPTT values within therapeutic aPTT goal while achieving similar clinical outcomes. Although not approved by the FDA for managing HIT, bivalirudin may be an attractive alternative anticoagulant.

Singleton {NOT} and Doubleton {YES; NOT} Gates Act as Functionally Complete Sets in DNA-Integrated Computational Circuits.

A functionally complete Boolean operator is sufficient for computational circuits of arbitrary complexity. We connected YES (buffer) with NOT (inverter) and two NOT four-way junction (4J) DNA gates to obtain IMPLY and NAND Boolean functions, respectively, each of which represents a functionally complete gate. The results show a technological path towards creating a DNA computational circuit of arbitrary complexity based on singleton NOT or a combination of NOT and YES gates, which is not possible in electronic computers. We, therefore, concluded that DNA-based circuits and molecular computation may offer opportunities unforeseen in electronics.

A Case of Cameron Lesions: An Overlooked Cause of Anemia in Patients With Gastrointestinal Bleeding and Hiatal Hernia.

Cameron lesions are rare causes of upper gastrointestinal bleeding (UGIB). The lesions are linear erosions or ulcers that develop in the sac of a hiatal hernia, which often go unnoticed in the upper gastrointestinal system, and are a prevalent cause of anemia resulting from iron deficiency. Postponed treatment can result in severe consequences such as potentially fatal hemorrhaging. Here, we present a case of a young woman who presented to the emergency room with recurrent gastrointestinal bleeding and severe microcytic anemia. The chest X-ray revealed a partial intrathoracic stomach, and a large hiatal hernia was subsequently confirmed in the CT scan of the abdomen and pelvis. The esophagogastroduodenal endoscopy indicated Los Angeles Classification System grade A reflux esophagitis and an 8 cm hiatal hernia with multiple Cameron ulcers with pigmented material and chronic non-erosive gastritis. Biopsies of the gastric body and antrum showed Helicobacter pylori-associated chronic active gastritis and intestinal metaplasia. An esophagus biopsy showed squamous esophageal mucosa with mild chronic inflammation. The patient was treated with a transfusion of three units of red blood cells, iron replenishment, and pantoprazole infusion and underwent hiatal hernia repair with mesh and Toupet fundoplication without any complications. After that, the patient was discharged and scheduled for follow-up with general surgery at the outpatient clinic.

Cognitive and functional change in skilled nursing facilities: Differences by delirium and Alzheimer's disease and related dementias.

BACKGROUND: Whether cognitive and functional recovery in skilled nursing facilities (SNF) following hospitalization differs by delirium and Alzheimer's disease related dementias (ADRD) has not been examined. OBJECTIVE: To compare change in cognition and function among short-stay SNF patients with delirium, ADRD, or both. DESIGN: Retrospective cohort study using claims data from 2011 to 2013. SETTING: Centers for Medicare and Medicaid certified SNFs. PARTICIPANTS: A total of 740,838 older adults newly admitted to a short-stay SNF without prevalent ADRD who had at least two assessments of cognition and function. MEASUREMENTS: Incident delirium was measured by the Minimum Data Set (MDS) Confusion Assessment Method and ICD-9 codes, and incident ADRD by ICD-9 codes and MDS diagnoses. Cognitive improvement was a better or maximum score on the MDS Brief Interview for Mental Status, and functional recovery was a better or maximum score on the MDS Activities of Daily Living Scale. RESULTS: Within 30 days of SNF admission, the rate of cognitive improvement in patients with both delirium/ADRD was half that of patients with neither delirium/ADRD (HR = 0.45, 95% CI:0.43, 0.46). The ADRD-only and delirium-only groups also were 43% less likely to have improved cognition or function compared to those with neither delirium/ADRD (HR = 0.57, 95% CI:0.56, 0.58 and HR = 0.57, 95% CI:0.55, 0.60, respectively). Functional improvement was less likely in patients with both delirium/ADRD, as well (HR = 0.85, 95% CI:0.83, 0.87). The ADRD only and delirium only groups were also less likely to improve in function (HR = 0.93, 95% CI:0.92, 0.94 and HR = 0.92, 95% CI:0.90, 0.93, respectively) compared to those with neither delirium/ADRD. CONCLUSIONS: Among older adults without dementia admitted to SNF for post-acute care following hospitalization, a positive screen for delirium and a new diagnosis of ADRD, within 7 days of SNF admission, were both significantly associated with worse cognitive and functional recovery. Patients with both delirium and new ADRD had the worst cognitive and functional recovery.

Neuropsychological test performance before and after HIV-1 seroconversion: the Multicenter AIDS Cohort Study.

The objective of this study is to compare neuropsychological test performance before and after HIV-1 seroconversion in order to identify possible acute changes in psychomotor speed, memory, attention, and concentration secondary to seroconversion. The study utilized mixed effects models to examine longitudinal neuropsychological test data. We conducted a nested cohort study of 362 male HIV-1 seroconverters enrolled in the Multicenter AIDS Cohort Study. We used linear mixed models with random subject effects to compare repeated neuropsychological test outcomes from 5 years before seroconversion to 2 years after seroconversion on the Trail Making Test (parts A and B), Symbol-Digit Test, Grooved Pegboard (dominant and non-dominant hands), Stroop Color-Interference Test, Rey Auditory Verbal Learning Test, and the CalCAP Reaction Time Test. We found no significant changes in the time-dependent score after seroconversion for the majority of neuropsychological tests used in the Multicenter AIDS Cohort Study. There was a significant change in time trend after seroconversion on part B of the Trail Making Test (p=0.042), but the difference only represented a 2 % decrease in performance. We found the following characteristics to be associated with worse neuropsychological test performance: lower education levels, history of depression, older age, and no previous neurocognitive testing (p< .05). Our results suggest that despite a 50 % decrease in CD4 cell count immediately following infection, HIV-1 does not appear to have a measurable effect on psychomotor or complex cognitive processing for up to 2 years following infection, using this set of neurocognitive measures.

Structure-Kinetics Relationships of Opioids from Metadynamics and Machine Learning.

The nation's opioid overdose deaths reached an all-time high in 2021. The majority of deaths are due to synthetic opioids represented by fentanyl. Naloxone, which is an FDA-approved reversal agent, antagonizes opioids through competitive binding at the mu-opioid receptor (mOR). Thus, knowledge of opioid's residence time is important for assessing the effectiveness of naloxone. Here we estimated the residence times of 15 fentanyl and 4 morphine analogs using metadynamics, and compared them with the most recent measurement of the opioid kinetic, dissociation, and naloxone inhibitory constants (Mann, Li et al, Clin. Pharmacol. Therapeut. 2022). Importantly, the microscopic simulations offered a glimpse at the common binding mechanism and molecular determinants of dissociation kinetics for fentanyl analogs. The insights inspired us to develop a machine learning (ML) approach to analyze the kinetic impact of fentanyl's substituents based on the interactions with mOR residues. This proof-of-concept approach is general; for example, it may be used to tune ligand residence times in computer-aided drug discovery.

Kinetics and Mechanism of Fentanyl Dissociation from the µ-Opioid Receptor.

Driven by illicit fentanyl, opioid related deaths have reached the highest level in 2020. Currently, an opioid overdose is resuscitated by the use of naloxone, which competitively binds and antagonizes the µ-opioid receptor (mOR). Thus, knowledge of the residence times of opioids at mOR and the unbinding mechanisms is valuable for assessing the effectiveness of naloxone. In the present study, we calculate the fentanyl-mOR dissociation time and elucidate the mechanism by applying an enhanced sampling molecular dynamics (MD) technique. Two sets of metadynamics simulations with different initial structures were performed while accounting for the protonation state of the conserved H2976.52, which has been suggested to modulate the ligand-mOR affinity and binding mode. Surprisingly, with the Nδ-protonated H2976.52, fentanyl can descend as much as 10 Å below the level of the conserved D1473.32 before escaping the receptor and has a calculated residence time τ of 38 s. In contrast, with the Nϵ- and doubly protonated H2976.52, the calculated τ are 2.6 and 0.9 s, respectively. Analysis suggests that formation of the piperidine-Hid297 hydrogen bond strengthens the hydrophobic contacts with the transmembrane helix (TM) 6, allowing fentanyl to explore a deep pocket. Considering the experimental τ of ∼4 min for fentanyl and the role of TM6 in mOR activation, the deep insertion mechanism may be biologically relevant. The work paves the way for large-scale computational predictions of opioid dissociation rates to inform evaluation of strategies for opioid overdose reversal. The profound role of the histidine protonation state found here may shift the paradigm in computational studies of ligand-receptor kinetics.

Impact of Early Introduction to the Neurosciences on West Virginia High School Students via the Brain Bee.

BACKGROUND: The science, technology, engineering, and math (STEM) fields are often underrepresented due to lack of interest or exposure. The Brain Bee is a neuroscience competition for high school students meant to inspire future leaders in the neurosciences. A regional Brain Bee competition hosted in West Virginia was led by medical students and neurology residents with the goal of increasing high school student interest in the neurosciences. ACTIVITY: The West Virginia Brain Bee competition consisted of a neuroanatomy practical, a written exam, and a clinical assessment. Other fun neuroscience educational activities were also offered to students throughout the competition day. Students were surveyed before and after the competition day. RESULTS: Student interest in pursuing a neuroscience career increased (3.24 to 3.58, p = 0.043), and confidence in neuroscience knowledge increased (2.88 to 3.12, p = 0.036). Qualitative assessment revealed the importance of role models and a supportive environment for student learning. CONCLUSION: The West Virginia Brain Bee increased high school student interest in and confidence of neuroscience knowledge. This competition may be a meaningful way to connect high school students with potential mentors in the neurosciences and may also help foster an interest in pursuing a career in the neurosciences in the future.

How µ-opioid receptor recognizes fentanyl.

Roughly half of the drug overdose-related deaths in the United States are related to synthetic opioids represented by fentanyl which is a potent agonist of mu-opioid receptor (mOR). In recent years, X-ray crystal structures of mOR in complex with morphine derivatives have been determined; however, structural basis of mOR activation by fentanyl-like opioids remains lacking. Exploiting the X-ray structure of BU72-bound mOR and several molecular simulation techniques, we elucidated the detailed binding mechanism of fentanyl. Surprisingly, in addition to the salt-bridge binding mode common to morphinan opiates, fentanyl can move deeper and form a stable hydrogen bond with the conserved His2976.52, which has been suggested to modulate mOR's ligand affinity and pH dependence by previous mutagenesis experiments. Intriguingly, this secondary binding mode is only accessible when His2976.52 adopts a neutral HID tautomer. Alternative binding modes may represent a general mechanism in G protein-coupled receptor-ligand recognition.

Utilization of cumulative antibiograms for public health surveillance: Trends in Escherichia coli and Klebsiella pneumoniae susceptibility, Massachusetts, 2008-2018.

BACKGROUND: Antimicrobial resistance is an urgent public health threat. Identifying trends in antimicrobial susceptibility can inform public health policy at the state and local levels. OBJECTIVE: To determine the ability of statewide antibiogram aggregation for public health surveillance to identify changes in antimicrobial resistance trends. DESIGN: Facility-level trend analysis. METHODS: Crude and adjusted trend analyses of the susceptibility of Escherichia coli and Klebsiella pneumoniae to particular antibiotics, as reported by aggregated antibiograms, were examined from 2008 through 2018. Multivariable regression analyses via generalized linear mixed models were used to examine associations between hospital characteristics and trends of E. coli and K. pneumoniae susceptibility to ciprofloxacin and ceftriaxone. RESULTS: E. coli and K. pneumoniae showed inverse trends in drug susceptibility over time. K. pneumoniae susceptibility to fluoroquinolones increased by 5% between 2008 and 2018 (P < .05). In contrast, E. coli susceptibility declined during the same period to ceftriaxone (6%), gentamicin (4%), and fluoroquinolones (4%) (P < .05). When compared to Boston hospitals, E. coli isolates from hospitals in other regions had a >4% higher proportion of susceptibility to ciprofloxacin and a >3% higher proportion of susceptibility to ceftriaxone (P < .05). Isolates of K. pneumoniae had higher susceptibility to ciprofloxacin (>3%) and ceftriaxone (>1.5%) in all regions when compared to Boston hospitals (P < .05). CONCLUSIONS: Cumulative antibiograms can be used to monitor antimicrobial resistance, to discern regional and facility differences, and to detect changes in trends. Furthermore, because the number of years that hospitals contributed reports to the state-level aggregate had no significant influence on susceptibility trends, other states should not be discouraged by incomplete hospital compliance.

How µ-Opioid Receptor Recognizes Fentanyl.

In 2019, drug overdose has claimed over 70,000 lives in the United States. More than half of the deaths are related to synthetic opioids represented by fentanyl which is a potent agonist of mu-opioid receptor (mOR). In recent years, the crystal structures of mOR in complex with morphine derivatives have been determined; however, structural basis of mOR activation by fentanyl-like synthetic opioids remains lacking. Exploiting the X-ray structure of mOR bound to a morphinan ligand and several state-of-the-art simulation techniques, including weighted ensemble and continuous constant pH molecular dynamics, we elucidated the detailed binding mechanism of fentanyl with mOR. Surprisingly, in addition to forming a salt-bridge with Asp1473.32 in the orthosteric site common to morphinan opiates, fentanyl can move deeper and bind mOR through hydrogen bonding with a conserved histidine His2976.52, which has been shown to modulate mOR's ligand affinity and pH dependence in mutagenesis experiments, but its precise role remains unclear. Intriguingly, the secondary binding mode is only accessible when His297 adopts a neutral HID tautomer. Alternative binding modes and involvement of tautomer states may represent general mechanisms in G protein-coupled receptor (GPCR)-ligand recognition. Our work provides a starting point for understanding the molecular basis of mOR activation by fentanyl which has many analogs emerging at a rapid pace. The knowledge may also inform the design of safer analgesics to combat the opioid crisis. Current protein simulation studies employ standard protonation and tautomer states; our work demonstrates the need to move beyond the practice to advance our understanding of protein-ligand recognition.

How mu-Opioid Receptor Recognizes Fentanyl.

The opioid crisis has escalated during the COVID-19 pandemic. More than half of the overdose-related deaths are related to synthetic opioids represented by fentanyl which is a potent agonist of mu-opioid receptor (mOR). In recent years, crystal structures of mOR complexed with morphine derivatives have been determined; however, structural basis of mOR activation by fentanyl-like synthetic opioids remains lacking. Exploiting the X-ray structure of mOR bound to a morphinan ligand and several state-of-the-art simulation techniques, including weighted ensemble and continuous constant pH molecular dynamics, we elucidated the detailed binding mechanism of fentanyl with mOR. Surprisingly, in addition to the orthosteric site common to morphinan opiates, fentanyl can move deeper and bind mOR through hydrogen bonding with a conserved histidine H297, which has been shown to modulate mOR's ligand affinity and pH dependence in mutagenesis experiments, but its precise role remains unclear. Intriguingly, the secondary binding mode is only accessible when H297 adopts a neutral HID tautomer. Alternative binding modes and involvement of tautomer states may represent general mechanisms in G protein-coupled receptor (GPCR)-ligand recognition. Our work provides a starting point for understanding mOR activation by fentanyl analogs that are emerging at a rapid pace and assisting the design of safer analgesics to combat the opioid crisis. Current protein simulation studies employ standard protonation and tautomer states; our work demonstrates the need to move beyond the practice to advance our understanding of protein-ligand recognition.

Treatment of Staphylococcus aureus skin infection in vivo using rifampicin loaded lipid nanoparticles.

We have previously reported on a novel nanoparticle formulation that was effective at killing Staphylococcus aureus in vitro. Here, we report for the first time, the antibacterial effects of a lipidic nano-carrier containing rifampicin (NanoRIF) which can be used to successfully treat Methicillin-Resistant S. aureus (MRSA) infection at a reduced antibiotic dosage compared to the free drug in a skin wound model in mice. The formulation used contains the lipid monoolein, a cationic lipid N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl-sulfate (DOTAP) and the antibiotic. We have shown that rifampicin-loaded nanoparticles are more effective at treating infection in the skin wound model than the antibiotic alone. Cryo-TEM was used to capture for the first time, interactions of the formed nanoparticles with the cell wall of an individual bacterium. Our data strongly indicate enhanced binding of these charged nanoparticles with the negatively charged bacterial membrane. The efficacy we have now observed in vivo is of significant importance for the continued development of nanomedicine-based strategies to combat antibiotic resistant bacterial skin infections.

Microscopic Behaviors of Tri- n-Butyl Phosphate, n-Dodecane, and Their Mixtures at Air/Liquid and Liquid/Liquid Interfaces: An AMBER Polarizable Force Field Study.

In solvent extraction processes for recovering metal ions from used nuclear fuel, as well as other industrial applications, a better understanding of the metal complex phase transfer phenomenon would greatly aid ligand design and process optimization. We have approached this challenge by utilizing the classical molecular dynamics simulations technique to gain visual appreciation of the vapor/liquid and liquid/liquid interface between tri- n-butyl phosphate (TBP) and n-dodecane with air and water. In this study, we successfully reparameterized polarizable force fields for TBP and n-dodecane that accurately reproduced several of their thermophysical properties such as density, heat of vaporization, and dipole moment. Our models were able to predict the surface and interfacial tension of different systems when compared to experimental results that were also performed by us. Through this study, we gained atomistic understanding of the behaviors of TBP and n-dodecane at the interface against air and water, useful in further computational studies of such systems. Finally, our studies indicate that the initial configuration of a simulation may have a large effect on the final result.