Predictive Power of the NSQIP Risk Calculator for Early Post-Operative Outcomes After Whipple: Experience from a Regional Center in Northern Ontario

Postoperative infectious complications worsen oncologic outcomes following pancreaticoduodenectomy for pancreatic ductal adenocarcinoma

BACKGROUND

Pancreaticoduodenectomy (PD) remains the only curative option for patients with pancreatic adenocarcinoma (PDAC). Infectious complications (IC) can negatively impact patient outcomes and delay adjuvant therapy in most patients. This study aims to determine IC effect on overall survival (OS) following PD for PDAC.

STUDY DESIGN

Patients who underwent PD for PDAC between 2010 and 2020 were identified from a single institutional database. Patients were categorized into two groups based on whether they experienced IC or not. The relationship between postoperative IC and OS was investigated using Kaplan-Meier and Cox-regression multivariate analysis.

RESULTS

Among 655 patients who underwent PD for PDAC, 197 (30%) experienced a postoperative IC. Superficial wound infection was the most common type of infectious complication (n = 125, 63.4%). Patients with IC had significantly more minor complications (Clavien-Dindo [CD] < 3; [59.4% vs. 40.2%, p < 0.001]), major complications (CD ≥ 3; [37.6% vs. 18.8%, p < 0.001]), prolonged LOS (47.2% vs 20.3%, p < 0.001), biochemical leak (6.1% vs. 2.8%, p = 0.046), postoperative bleeding (4.1% vs. 1.3%, p = 0.026) and reoperation (9.6% vs. 2.2%, p < 0.001). Time to adjuvant chemotherapy was delayed in patients with IC versus those without (10 vs. 8 weeks, p < 0.001). Median OS for patients who experienced no complication, noninfectious complication, and infectious complication was 33.3 months, 29.06 months, and 27.58 months respectively (p = 0.023). On multivariate analysis, postoperative IC were an independent predictor of worse OS (HR 1.32, p = 0.049).

CONCLUSIONS

IC following PD for PDAC independently predict worse oncologic outcomes. Thus, efforts to prevent and manage IC should be a priority in the care of patients undergoing PD for PDAC.

Outpatient compared to inpatient thyroidectomy on 30-day postoperative outcomes: a national propensity matched analysis

BACKGROUND

To address the postoperative outcomes between outpatient and inpatient neck surgery involving thyroidectomy procedures.

METHODS

A cohort analysis of surgical patients undergoing primary, elective, total thyroidectomy from multiple United States medical institutions who were registered with the American College of Surgeons National Surgical Quality Improvement Program from 2015 to 2018. The primary outcome was a composite score that included any 30-day postoperative adverse event.

RESULTS

A total of 55,381 patients who underwent a total thyroidectomy were identified comprising of 14,055 inpatient and 41,326 outpatient procedures. A cohort of 13,496 patients who underwent outpatient surgery were propensity matched for covariates with corresponding number of patients who underwent inpatient thyroidectomies. In the propensity matched cohort, the occurrence of any 30-day after surgery complications were greater in the inpatient group, 424 out of 13,496 (3.1%) compared to the outpatient group, 150 out of 13,496 (1.1%), P < 0.001. Moreover, death rates were greater in the inpatient group, 22 out 13,496 (0.16%) compared to the outpatient group, 2 out of 13,496 (0.01%), P < 0.001. Similarly, hospital readmissions occurred with greater frequency in the inpatient group, 438 out of 13,496 (3.2%) compared to the outpatient group, 310 out of 13,496 (2.3%), P < 0.001.

CONCLUSION

Thyroidectomy procedures performed in the outpatient setting had less rates of adverse events, including serious postoperative complications (e.g., surgical site infection, pneumonia, progressive renal insufficiency). In addition, patients who had thyroidectomy in the outpatient setting had less 30-day readmissions and mortality. Surgeons should recognize the benefits of outpatient thyroidectomy when selecting disposition of patients undergoing neck surgery.

Hypertension Requiring Medication Use: a Silent Predictor of Poor Outcomes After Pancreaticoduodenectomy

BACKGROUND

Although hypertension requiring medication (HTNm) is a well-known cardiovascular comorbidity, its association with postoperative outcomes is understudied. This study aimed to evaluate whether preoperative HTNm is independently associated with specific complications after pancreaticoduodenectomy.

STUDY DESIGN

Adults undergoing elective pancreaticoduodenectomy were included from the 2014-2019 NSQIP-targeted pancreatectomy dataset. Multivariable regression models compared outcomes between patients with and without HTNm. Endpoints included significant complications, any complication, unplanned readmissions, length of stay (LOS), clinically relevant postoperative pancreatic fistula (CR-POPF), and cardiovascular and renal complications. A subgroup analysis excluded patients with diabetes, heart failure, chronic obstructive pulmonary disease, estimated glomerular filtration rate from serum creatinine (eGFRCr) < 60 ml/min per 1.73 m², bleeding disorder, or steroid use.

RESULTS

Among 14,806 patients, 52% had HTNm. HTNm was more common among older male patients with obesity, diabetes, congestive heart failure, chronic obstructive pulmonary disease, functional dependency, hard pancreatic glands, and cancer. After adjusting for demographics, preoperative comorbidities, and laboratory values, HTNm was independently associated with higher odds of significant complications (aOR 1.12, p = 0.020), any complication (aOR 1.11, p = 0.030), cardiovascular (aOR 1.78, p = 0.002) and renal (aOR 1.60, p = 0.020) complications, and unplanned readmissions (aOR 1.14, p = 0.040). In a subgroup analysis of patients without major preoperative comorbidity, HTNm remained associated with higher odds of significant complications (aOR 1.14, p = 0.030) and cardiovascular complications (aOR 1.76, p = 0.033).

CONCLUSIONS

HTNm is independently associated with cardiovascular and renal complications after pancreaticoduodenectomy and may need to be considered in preoperative risk stratification. Future studies are necessary to explore associations among underlying hypertension, specific antihypertensive medications, and postoperative outcomes to investigate potential risk mitigation strategies.

Preparing for participation in the centers for Medicare and Medicaid Services' bundle care payment initiative-advanced for major bowel surgery

BACKGROUND

As healthcare costs rise, there is an increasing emphasis on alternative payment models to improve care efficiency. The bundled payment represents an alternative reimbursement model gaining popularity within the surgical sphere. We aimed to assess where the largest opportunities for care improvement lay and how best to identify patients at high risk of suffering costly complications.

METHODS

We utilized itemized CMS claims data for a retrospective cohort of patients between 2014 and 2016 who met inclusion criteria for the Major Bowel Bundled Payment Program and performed a cost analysis to identify opportunities for improved care efficiency. Based on the results of this cost analysis, we identified readmissions as a target for improvement. We then assessed whether the American College of Surgeons' National Surgical Quality Improvement Program surgical risk calculator (ACS NSQIP SRC) could accurately identify patients within our bundled payment population who were at high risk of readmission using a logistic regression model.

RESULTS

Our study cohort included 252 patients. Readmissions accounted for 12.8% of the average total care episode cost with a coefficient of variation of 2.72, thereby representing the most substantial, non-fixed cost for our bundled payment patients. Patients readmitted within their 90-day care episode were 2.53 times more likely to be high-cost (>$60,000) than patients not readmitted. However, the ACS NSQIP SRC did not accurately predict patients at high risk of readmission within the first 30 days with an AUROC of 0.58.

CONCLUSIONS

Our study highlights the importance of reducing readmissions as a central component of improving care for bowel surgery bundled payment patients. Preventing such readmissions requires accurate identification of patients at high risk of readmission; however, current risk prediction models lack the adaptability necessary for this task.

The association between vital signs abnormalities during postanaesthesia care unit stay and deterioration in the general ward following major abdominal cancer surgery assessed by continuous wireless monitoring

Objective: Vital signs abnormalities in the post-anaesthesia care unit (PACU) may identify patients at risk of severe postoperative complications in the general ward, but are sparsely investigated by continuous monitoring. We aimed to assess if the severity of vital signs abnormalities in the PACU was correlated to the duration of severe vital signs abnormalities and serious adverse events (SAEs) in the general ward. Design: Prospective cohort study. Primary exposure was PACU vital signs abnormalities assessed by a standardised PACU recovery score. Participants: Adult patients, aged ≥ 60 years, who underwent major abdominal cancer surgery. Main outcome measures: The duration of severe vital signs abnormalities were assessed by continuous wireless vital signs monitoring and, secondly, by any SAE within the first 96 hours in the general ward. Results: One-hundred patients were included, and 92 patients with a median of 91 hours (interquartile range, 71-95 hours) of vital signs recording were analysed. The maximum vital signs abnormalities in the PACU were not significantly correlated to overall vital signs abnormalities in the general ward (R = 0.13; P = 0.22). Severe circulatory abnormalities in the overall PACU stay and at discharge were significantly correlated to the duration of circulatory vital signs abnormalities on the ward (R = 0.32 [P = 0.00021] and R = 0.26 [P = 0.014], respectively). Seventeen patients (18%) experienced SAEs, without significant association to the PACU stay (area under the receiver operating characteristic [AUROC], 0.59; 95% CI, 0.46-0.73). Conclusion: Vital signs abnormalities in the PACU did not show a tendency towards predicting overall severe vital signs abnormalities or SAEs during the first days in the general ward. Circulatory abnormalities in the PACU showed a tendency towards predicting circulatory complications in the ward.

Inaccurate Risk Assessment by the ACS NSQIP Risk Calculator in Aortic Surgery

OBJECTIVES

The aim of this retrospective study was to assess the predictive performance of the American College of Surgeons (ACS) risk calculator for aortic aneurysm repair for the patient population of a Dutch tertiary referral hospital.

METHODS

This retrospective study included all patients who underwent elective endovascular or open aortic aneurysm repair at our institution between the years 2013 and 2019. Preoperative patient demographics and postoperative complication data were collected, and individual risk assessments were generated using five different current procedural terminology (CPT) codes. Receiver operating characteristic (ROC) curves, calibration plots, Brier scores, and Index of Prediction Accuracy (IPA) values were generated to evaluate the predictive performance of the ACS risk calculator in terms of discrimination and calibration.

RESULTS

Two hundred thirty-four patients who underwent elective endovascular or open aortic aneurysm repair were identified. Only five out of thirteen risk predictions were found to be sufficiently discriminative. Furthermore, the ACS risk calculator showed a structurally insufficient calibration. Most Brier scores were close to 0; however, comparison to a null model though IPA-scores showed the predictions generated by the ACS risk calculator to be inaccurate. Overall, the ACS risk calculator showed a consistent underestimation of the risk of complications.

CONCLUSIONS

The ACS risk calculator proved to be inaccurate within the framework of endovascular and open aortic aneurysm repair in our medical center. To minimize the effects of patient selection and cultural differences, multicenter collaboration is necessary to assess the performance of the ACS risk calculator in aortic surgery.

Length of Stay After Joint Arthroplasty is Less Than Predicted Using Two Risk Calculators

BACKGROUND

Predicting the length of stay (LOS) after total joint arthroplasty (TJA) has become more important with their recent removal from inpatient-only designation. The American College of Surgeons (ACS) National Surgical Quality Improvement Program surgical risk calculator and the CMS' diagnosis-related group (DRG) calculator are two common LOS predictors. The aim of our study was to determine how our actual LOS compared with those predicted by both the ACS and DRG.

METHODS

99 consecutive TJA (49 hips and 50 knee procedures) were reviewed in Medicare-eligible patients from four fellowship-trained arthroplasty surgeons. Predicted LOS was calculated using the DRG and ACS risk calculators for each patient using demographics, medical histories, and comorbidities. LOS was compared between the predicted and the actual LOS for both total hip arthroplasty (THA) and total knee arthroplasty (TKA) using paired t-tests.

RESULTS

Actual LOS was shorter in the THA group vs the TKA group (1.29 days vs 1.46 days, P < .05). The actual LOS of patients at our institution was significantly shorter than both DRG and ACS predictions for both THA and TKA (P < .05). In both the THA and TKA patients, the actual LOS (1.29 and 1.46 day) was significantly shorter than the DRG-predicted LOS (2.15 and 2.15 days) which was significantly shorter than the ACS-predicted LOS (2.9 and 3.14 days).

CONCLUSION

We found the actual LOS was significantly shorter than that predicted by both the DRG and ACS risk calculators. Current risk calculators may not be accurate for contemporary fast-track protocols and newer tools should be developed.

Evaluating Postoperative Morbidity in Patients Undergoing Pelvic Reconstructive Surgery Using the American College of Surgeons National Surgical Quality Improvement Program Surgical Risk Calculator

OBJECTIVE

The aim of this study was to evaluate the ability of the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) surgical risk calculator to predict surgical morbidity in patients undergoing pelvic reconstructive surgery.

METHODS

This was a retrospective study of patients who underwent pelvic reconstructive surgery from 2014 to 2017. Preoperative risk factors were abstracted from medical records and entered into the ACS NSQIP surgical risk calculator. The Current Procedural Terminology code that produced the largest risk was used and compared with actual patient outcomes. Demographic, clinical, and surgical characteristics were analyzed descriptively. Logistic regression evaluated significant factors associated with each outcome; prediction capability of the risk calculator was assessed.

RESULTS

Seven hundred thirty-one surgical cases were reviewed. The cohort was predominantly younger than 65 years (58.7%), white (77.4%), multiparous (81.1%), and overweight (64.7%); 76.3% were American Society of Anesthesiologists class 2, and 70.2% had vaginal surgery. There was no difference in median risk scores between those with and without postoperative event. Two hundred twenty-one (30.3%) experienced "any serious complication," with 89% of these due to urinary tract infection. Incidence of urinary tract infection was 27%; readmission was 3.2%, and 3.6% returned to the operating room. Decreasing age was predictive of return to the operating room (P < 0.001), and increasingly worse functional status predicted discharge to nursing or skilled rehabilitation facility (P < 0.001).

CONCLUSIONS

The ACS NSQIP surgical risk calculator is an overall poor predictor of actual outcomes in a sample of patients who underwent pelvic reconstructive surgery, perhaps because of low prevalence of serious events. A more accurate surgical risk calculator is needed for this patient population.

Development of a Novel Pancreatoduodenectomy-Specific Risk Calculator: an Analysis of 10,000 Patients

BACKGROUND

Pancreatoduodenectomy (PD) is often performed in frail patients and is associated with significant morbidity. The five-factor modified frailty index (mFI-5) has been utilized to predict adverse postoperative outcomes, but has not been tested in PD. We aimed to develop risk tools to generate and predict 30-day outcomes after PD and compare their performance with the mFI-5. Risk tools were then used to generate a PD-specific calculator.

METHODS

Elective PDs from the 2014-2016 ACS NSQIP® Procedure Targeted Pancreatectomy PUFs were identified. Multivariable logistic regression models were constructed to predict postoperative mortality, any complication, serious complication, clinically relevant postoperative pancreatic fistula (CR-POPF), and discharge not-to-home. Predictive accuracy was evaluated through repeated stratified tenfold cross-validation and compared to the mFI-5.

RESULTS

Nine thousand eight hundred sixty-seven PDs were captured. Nine risk factors were retained: sex, age, BMI, DM, HTN, ASA classification, pancreatic duct size, gland texture, and adenocarcinoma. Cross-validated C-indices ranged from 0.49 to 0.61 for the mFI-5 and 0.63 to 0.75 for our risk models. The best-performing model was for discharge not-to-home (C = 0.75), and the model delivering the largest increase in predictive accuracy was for CR-POPF (C_mFI-5/Model = 0.49/0.70). A user-friendly risk calculator was created predicting the five outcomes of interest.

CONCLUSION

We have created a PD-specific risk calculator that outperforms the mFI-5. This calculator may serve as a useful adjunct in shared decision-making for patients and surgeons.

Risk assessment in aortic aneurysm repair by medical specialists versus the American College of Surgeons National Surgical Quality Improvement Program risk calculator outcomes

Objective

The aim of this online clinical vignette-based survey study was to compare risk assessments by vascular surgeons, anaesthesiologists and interventional radiologists involved in treating patients with aortic aneurysms in the Netherlands with the NSQIP risk calculator outcomes.

Methods

Participants, recruited using purposive sampling, provided their estimation of the likelihood of postoperative complications and events following aortic surgery in five fictional cases. These cases were subsequently scored using the NSQIP calculator. The risk assessments were statistically analysed using the ANOVA and student t-test.

Results

All participating specialists i.e. twelve vascular surgeons, ten interventional radiologists and ten anaesthesiologists completed the survey. In the vast majority of outcomes and vignettes, no significant differences were found between various specialists, whereas significant differences were found between the NSQIP risk calculator outcomes and the combined risk assessments of the specialists. Overall, specialist risk assessments differ from the NSQIP, but neither particularly higher nor lower compared to the risk calculator.

Conclusions

Risk assessment by vascular surgeons, anaesthesiologists and interventional radiologists differs significantly with NSQIP risk calculator outcomes, within the framework of both endovascular and open aortic aneurysm repair. Based on these results, implementing the NSQIP risk calculator in preoperative workup could be of added value in both patient planning as well as adequately informing patients for obtaining consent.

Risk-adjustment models in patients undergoing head and neck surgery with reconstruction

BACKGROUND

With the current focus on value-based outcomes and reimbursement models, perioperative risk adjustment is essential. Specialty surgical outcomes are not well predicted by the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP); the Head and Neck-Reconstructive Surgery NSQIP was created as a specialty-specific platform for patients undergoing head and neck surgery with flap reconstruction. This study aims to investigate risk prediction models in these patients.

METHODS

The Head and Neck-Reconstructive Surgery NSQIP collected data on patients undergoing head and neck surgery with flap reconstruction from August 1, 2012 to October 20, 2016. Multivariable logistic regression models were created for 9 outcomes (postoperative ventilator dependence, pneumonia, superficial recipient surgical site infection, presence of tracheostomy/nasoenteric (NE)/gastrostomy/gastrojejunostomy(G/GJ) tube 30 days postoperatively, conversion from NE to G/GJ tube, unplanned return to the operating room, length of stay > 7 days). External validation was completed with a more contemporary cohort.

RESULTS

A total of 1095 patients were included in the modelling cohort and 407 in the validation cohort. Models performed well predicting tracheostomy, NE, G/GJ tube presence at 30 days postoperatively and conversion from NE to G/GJ tube (c-indices = 0.75-0.91). Models for postoperative pneumonia, superficial recipient surgical site infection, ventilator dependence > 48 h, and length of stay > 7 days were fair (concordance [c]-indices = 0.63-0.69). The predictive model for unplanned return to the operating room was poor (c-index = 0.58).

CONCLUSIONS AND RELEVANCE

Reliable and discriminant risk prediction models were able to be created for postoperative outcomes using the specialty-specific Head and Neck-Reconstructive Surgery Specific NSQIP.

Efficacy and utility of robotic single-access bilateral nephrectomy (r-SABN) in end-stage renal disease patients

PURPOSE

Bilateral native nephrectomies are needed in ESRD patients with select indications in a pre-transplant setting. Yet, the perioperative morbidity is significant in this population. Herein we evaluate the efficacy and utility of r-SABN.

METHOD

A total of 12 patients were consented at a single center. Of 12 patients, 3 patients did not meet study criteria and were excluded. Preoperative, perioperative, and postoperative data were prospectively collected from 9 patients from electronic health records and administered postoperative surveys. Patients were assessed at 30-180 days postoperatively for follow-up.

RESULTS

Mean operative time was 204.3 ± 59.7 min (142.0-314.0) and estimated blood loss during operation was 94.4 ± 87.3 ml (25.0-300.0). The mean length of hospital stay was 2 ± 0.7 days (1-3) for all patients. Total post-operative opioid usage was normalized to morphine dose equivalents (MDE) and calculated to be 56.1 ± 30.4 mg (30.8-101.8). Patients experienced a fourfold and tenfold respective increase in weekly structural and incidental physical activity from 30 to 180 days postoperatively. There were no procedure related intraoperative or postoperative complications reported in the cohort.

CONCLUSION

Overall, r-SABN afforded the patients low morbidity. Longitudinal studies are in progress to further assess the efficacy and outcome of this procedure. In a single-center study, we demonstrate r-SABN is viable and provides a novel tool for treatment of ESRD patients requiring this procedure.

Evaluating the ACS NSQIP Risk Calculator in Primary Pancreatic Neuroendocrine Tumor: Results from the US Neuroendocrine Tumor Study Group

BACKGROUND

In a changing health care environment where patient outcomes will be more closely scrutinized, the ability to predict surgical complications is becoming increasingly important. The American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) online risk calculator is a popular tool to predict surgical risk. This paper aims to assess the applicability of the ACS NSQIP calculator to patients undergoing surgery for pancreatic neuroendocrine tumors (PNETs).

METHODS

Using the US Neuroendocrine Tumor Study Group (USNET-SG), 890 patients who underwent pancreatic procedures between 1/1/2000-12/31/2016 were evaluated. Predicted and actual outcomes were compared using C-statistics and Brier scores.

RESULTS

The most commonly performed procedure was distal pancreatectomy, followed by standard and pylorus-preserving pancreaticoduodenectomy. For the entire group of patients studied, C-statistics were highest for discharge destination (0.79) and cardiac complications (0.71), and less than 0.7 for all other complications. The Brier scores for surgical site infection (0.1441) and discharge to nursing/rehabilitation facility (0.0279) were below the Brier score cut-off, while the rest were equal to or above and therefore not useful for interpretation.

CONCLUSION

This work indicates that the ACS NSQIP risk calculator is a valuable tool that should be used with caution and in coordination with clinical assessment for PNET clinical decision-making.

Experiences with the standardized classification of surgical complications (Clavien-Dindo) in general surgery patients

Background

The standardized Clavien-Dindo classification of surgical complications is applied as a simple and widely used tool to assess and report postoperative complications in general surgery. However, most documentation uses this classification to report surgery-related morbidity and mortality in a single field of surgery or even particular intervention. The aim of the present study was to present experiences with the Clavien-Dindo classification when applied to all patients on the general surgery ward of a tertiary referral care center.

Methods

We analyzed a period of 6 months of care on a ward with a broad range of general and visceral surgery. Discharge reports and patient charts were analyzed retrospectively and reported complications rated according to the most recent Clavien-Dindo classification version. The complexity of operations was assessed with the Austrian Chamber of Physicians accounting system.

Results

The study included 517 patients with 817 admissions, of whom 463 had been operated upon. Complications emerged in 12.5%, of which 19% were rated as Clavien I, 20.7% as Clavien II, 13.8% as Clavien IIIa, 27.6% as Clavien IIIb, 8.6% as Clavien IVa, and 10.3% as Clavien V. No Clavien grade IVb complication occurred within the investigation. Patients having undergone more complex surgery or with higher scores experienced significantly longer lengths of hospital stay.

Conclusion

The Clavien-Dindo classification can easily be used to document complication rates in general surgery, even though this collective was not included in the original validation studies of Clavien et al. and consisted of more heavily impaired patients.

The American College of Surgeons National Surgical Quality Improvement Program Surgical Risk Calculator Has a Role in Predicting Discharge to Post-Acute Care in Total Joint Arthroplasty

BACKGROUND

Patient demand and increasing cost awareness have led to the creation of surgical risk calculators that attempt to predict the likelihood of adverse events and to facilitate risk mitigation. The American College of Surgeons National Surgical Quality Improvement Program Surgical Risk Calculator is an online tool available for a wide variety of surgical procedures, and has not yet been fully evaluated in total joint arthroplasty.

METHODS

A single-center, retrospective review was performed on 909 patients receiving a unilateral primary total knee (496) or hip (413) arthroplasty between January 2012 and December 2014. Patient characteristics were entered into the risk calculator, and predicted outcomes were compared with observed results. Discrimination was evaluated using the receiver-operator area under the curve (AUC) for 90-day readmission, return to operating room (OR), discharge to skilled nursing facility (SNF)/rehab, deep venous thrombosis (DVT), and periprosthetic joint infection (PJI).

RESULTS

The risk calculator demonstrated adequate performance in predicting discharge to SNF/rehab (AUC 0.72). Discrimination was relatively limited for DVT (AUC 0.70, P = .2), 90-day readmission (AUC 0.63), PJI (AUC 0.67), and return to OR (AUC 0.59). Risk score differences between those who did and did not experience discharge to SNF/rehab, 90-day readmission, and PJI reached significance (P < .01). Predicted length of stay performed adequately, only overestimating by 0.2 days on average (rho = 0.25, P < .001).

CONCLUSION

The American College of Surgeons National Surgical Quality Improvement Program Surgical Risk Calculator has fair utility in predicting discharge to SNF/rehab, but limited usefulness for 90-day readmission, return to OR, DVT, and PJI. Although length of stay predictions are similar to actual outcomes, statistical correlation remains relatively weak.