Re-analysis and generation of Overstay2 model

This page is about the development of the model for generating scores/colours for Project Overstay2. Since our data collection and the healthcare system changed since the first iteration, we did a re-analysis and generation of Overstay2 model, resulting in the Overstay2 scoring models that generate the Overstay2 colour. Also see the Overstay2 Overview.

Defining the contributing factors data

The model depends on a regression analysis of a number of possible factors in our regularly collected data. Our data structure had changed since the original project, so we cleaned up our definitions, resulting in the Data definition for factor candidates for the Overstay2 project.

Still needs: considerations values we considered and rejected minimize duplication of Data definition for factor candidates for the Overstay2 project, things that users of the data need to know going forward need to live there, decisions taken that don't affect ongoing process should be documented here.

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Model dataset and date range

• Dataset: We used the file 2025-2-3_13.56.31_Centralized_data.accdb as a basis for the project. A copy for future reference is at
  • \\ad.wrha.mb.ca\WRHA\HSC\shared\MED\MED_CCMED\Julie\MedProjects\Overstay_Project_2025

• Reference Admit DtTm: We based the date range on the first medicine admit date during a Data definition for factor candidates for the Overstay2 project#Hospitalization, based on the earliest Boarding Loc dttm.

• Dataset inclusion criteria: (all/and) of the following
  • Reference Admit DtTm >=2020-11-01 and <2025-01-01
  • RecordStatus = Vetted
  • final dispo of the Data definition for factor candidates for the Overstay2 project#Hospitalization is to a destination outside of the hospital of the admission (can be to other hospital)
  • HOBS: include the record only if:
    • the first medicine admission during a hospitalization is on a HOBS unit, and
    • there is a Transfer_Ready_Dttm associated with that unit, and
    • the patient is discharged from that unit to a a destination outside of the hospital of the admission (can be to other hospital)

• This resulted in a dataset with the following:
  • Total hospitalizations: 42,078

Site	Data Set	Total	Overstay >= 10d	Overstay < 10 days
All	All	42,078	1741 (4.1%)	40,337 (95.9%)
All	Training	21,054	859 (4.1%)	20,195 (95.9%)
All	Validation	21,024	882 (4.2%)	20,142 (95.8%)
HSC	All	16,813	616 (3.7%)	16,197 (96.3%)
HSC	Training	8,371	295 (3.5%)	8,076(96.5%)
HSC	Validation	8,442	321 (3.8%)	8,121 (96.2%)
SBGH	All	13,762	398 (2.9%)	13,364 (97.1%)
SBGH	Training	6,905	204 (3.0%)	6,701 (97.0%)
SBGH	Validation	6,857	194 (2.8%)	6,663 (97.2%)
GGH	All	11,503	727 (6.3%)	10,776 (93.7%)
GGH	Training	5,778	360 (6.2%)	5,418 (93.8%)
GGH	Validation	5,725	367 (6.4%)	5,358 (93.6%)

The SAS code defining this dataset can be found in S:\MED\MED_CCMED\Julie\MedProjects\Overstay_Project_2025\Data\prepdata_7Feb2025.sas

The CFE code defining this dataset

still needs to be set up by Tina...

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Specific decisions were discussed and made.

JM had found Vetted n=226 cases with Last discharge DtTm (in ICU or Med) after 2024 until Feb 3,2025. Only 13 did not leave own site, 19 expired, 194 left the site. From the 213, some are long stayed patients admitted Aug –1, Sept-3, Oct-8, Nov-18, Dec=196. (DR agreed in the meeting with JM Feb10). First Med Admits who were RecordStatus = incomplete but with Dispo DtTm present are excluded. First Med Admits who were still in the unit are excluded (ie no Dispo DtTm) First Med Admits who were RecordStatus = vetted are included. Deceased should be included: I think there was talk about excluding these; I don’t think that is valid. We don’t know when they arrive that they will die, and if they die after becoming transfer ready that is still an overstay we could have avoided. Discharge to or Previous Location = Hospice should be included – for the same reason we would include PCH. Palliative patients should be included because our definition “Palliative care” (ICD10 Z51.5) doesn’t imply death is imminent. Palliative patients were excluded before, but our definition has changed, and how this appears to be handled now has as well. Also, they may be waiting in hospital for a hospice, so again, that’s overstay. Discharged to STB Palliative Care - -included (DR agreed in the meeting with JM feb10) AMA – include these. Initial thought was that AMA implies they were not discharge ready, but it could also include those who were sick of waiting for a PCH and walked out. They might just be someone who waited for 2 weeks while dispo ready and eventually ran away because they did not want to wait for home care or etc any longer. But can someone be transfer ready and still leave AMA? Yes, e.g. when they were transfer ready but the discharge took so long that they no longer are and now can leave AMA again. JM found 3061 dispo AMA (2810 wo TR_dt, 251 w TR_Dt) Dispo TCU/TCE – include, and treat as discharge from this hospital Dispo HSC Lennox Bell/Institution NOS – treat as we would back-to-PCH/home Dispo another ward within WPG (LAU at CON, OAKS, VIC)? – include, and treat as discharge from this hospital Unknown disposition at discharge on the last admission – those transferred to another service (ICU/ OR/ etc within the same hospital - already excluded with RecordStatus = ”incomplete” and by only including if (1c) Dispo Transfers to different hospital ICU within Winnipeg – include Transfers outside WPG – include and treat as if discharged Overstay 5 to 9 days - included as normal (Rodrigo excluded these from model building) A null Tr_DtTm will be allowed This defines “hospitalization” as per-site, so if the patient is moved to subsequent medicine wards at a different hospital there will be a new record EMIP / TR_DtTm during ED portion of visit: treat this as you would on the ward. The First TR DTtm at ER will be taken regardless whether there is a second TR dttm when patient moved to a Med Med ward (DR agreed in the meeting with JM Feb10)

Model development Inclusion/Exclusion of "Green" admissions

If we plan to generate overstay colours like the last time, then the one group who would not have the model applied to them would be the “greens”, since the decision tree turns them green before the model would be applied. If we were able to determine who these greens would have been, would we want to exclude them from the model?

There is no way to exclude the greens from the model, so we won’t try.

Analysis and model generation

Parameter candidates

See Data definition for factor candidates for the Overstay2 project for the definitions.

Location Grouping considerations

When I looked at your code that breaks out Location / living arrangement into groupings and measures it seemed to me that it was mixing up data cleaning and validation with measure definition and it might be good to keep those separate. Cleaning and validation should apply to the data in general, not just this model, no? It would make sense to document the steps taken and things found and remedies implemented on this page, but having them part of the definition seems problematic. I think I sent that as an email, but I think it would be better to track this on the wiki to have a trail for the decisions. Ttenbergen 12:03, 25 June 2025 (CDT)

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reference/examples for links

leaving these here as examples how to link to the definitions on Data definition for factor candidates for the Overstay2 project. The currently used definition should live there, but changes and reasons should probably live here. We can change that format, talk to me if needed. Ttenbergen 11:35, 25 June 2025 (CDT)

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• Age
• PCH/Chronic Care
• other Location / living arrangement
• ADL components and
  • ADL_Adlmean_NH - among those who came from PCH/CHF
  • ADL_Adlmean_age - interaction with Age
• Glasgow Coma Scale
• Location / living arrangement Postal Code (also see [[#Location Grouping for Postal Code is N/A]])
• Charlson Diagnoses (Categories and Total Score)
  • MI, CHF, PVD, CVA , Pulmonary, Connective, Ulcer, Renal
  • Charlson Comorbidity Index
  • Charlson Score * NH - among those who came from PCH/CHF
• Diagnoses that might prevent/delay meeting PCH/Home Care criteria
• Homeless

Location Grouping for Postal Code is N/A

Analysis notes: JM found postal code N/A =2759, JM used the R_Province, Pre_inpt_Location, Previous Location instead to define the 5 categories above. Also encountered no match in the Postal_Code_Master List but was able to categorized based on the first 3 characters (N=273) - list given to Pagasa to add. (DR agreed in the meeting with JM Feb10)

Dataset split into training and validation data

We separated the population into two datasets based on the odd/even status of the last digit of the Chart number:

• Even: Training set
• Odd: validation set

Model generation and testing

See \\ad.wrha.mb.ca\WRHA\HSC\shared\MED\MED_CCMED\Julie\MedProjects\Overstay_Project_2025 and emails between Julie, Tina and Dan Roberts ~2025-02

Decision on a model

• For each site's training set and validation set, perform chi square test for independence between the variable OS (Overstay >= 10days and Overstay < 10d) and each factors listed Data definition for factor candidates for the Overstay2 project to identify the factors that may affect the overstay individually.
• Training data set - Methodology to find the best model involves
  • Basic plan for selecting the variables for the model -
    • Perform logistic model with the OS as the dependent variable and the independent variables beginning with the results from univariable analysis above and
    • Then by multivariable analysis using all independent variables (full model) and select via stepwise procedure both forward and backward selection.
    • Examine the importance of each variable included based on the probability result of its coefficient.
    • Those not contributing to the model are eliminated and new model is fitted. The process of deleting, refitting and verifying continues until it appears that all important variables are already included.
  • Assess the adequacy of the model both in terms of the individual variables and its overall fit by the following :
    • Estimated coefficients showing p-values of < 0.05 or having clinical relevance with p-values higher or close to 0.05 are included in the model.
    • The association of the predicted probabilities and observed responses is calculated by the Concordance (C) index and area under the curve (AUC) between the true positive rate (sensitivity) and false positive rate (1-specificity). A value > 0.5 implies ability to discriminate the positive and negative outcomes while a value 1 implies perfect classification. This quantity indicates how well the model ranks predictions .
    • The Hosmer-Lemeshow Goodness-of-fit test is used to assess how well the logistic regression model fits the data. A high p-value (usually > 0.05) means the model fits well while a low p-value (≤ 0.05) indicates poor fit of the model to the data.
• Validation data set involves:
  • Using the candidate models from the training data set - fit the model using the validation data set.
  • From the predicted values, determine the Concordance (C) index and area under the curve (AUC) between the true positive rate (sensitivity) and false positive rate (1-specificity). It must result to values closer to 1.
  • Group the predicted data into deciles (10 groups) and for each group, the observed number of events is compared to the expected number of events predicted by the model. The sum of these 10 groups called Chi-square statistic with 8 degrees of freedom must have p-value > 0.05 to denote good fit.
• If both the training data set and validation data set gave good results in all tests, then the model is a candidate for selection. If there are more than one candidate models, the one having more clinical relevance is opted.

• This resulted in Overstay2 scoring models by site.

Decision on a probability threshold

The predictive models we established are used to stratify the patient population for different Overstay2 processes on the units to reduce discharge delay. Details about establishing a threshold for the probabilities of the Overstay2 scoring models are in

• Overstay2 colour.