Model Parameters

What does the model need to run?

Hospital Parameters

Regional Population

The total population size of the catchment region of your hospital(s).

This is the initial S (Susceptible) input in the SIR model. This will affect projections for the number infected and the numbers requiring hospitalization, intensive care (ICU), and ventilation.

For Penn Medicine, this includes Delaware, Montgomery, Bucks, and Philadelphia counties.

Hospital Market Share (%)

The proportion of patients in the region that are likely to come to your hospital (as opposed to other hospitals in the region) when they get sick.

An estimate of this value can be to use the percentage of beds in your hospital compared to the total beds in your region.

Note: Your hospital's share may change over time, as the capacity of different hospitals to adapt to the scope epidemic may vary.

Currently Hospitalized COVID-19 Patients

The number of patients currently hospitalized with COVID-19 at your hospital(s).

This number is used in conjunction with Hospital Market Share and Hospitalization % to estimate the total number of infected individuals in your region.

Spread and Contact Parameters

Date of the first hospitalized case (Checkbox)

Use this checkbox to specify the date of the first hospitalized case within your hospital(s).

This date is used in conjunction with the current number of hospitalized patients to calculate doubling time and R0.

Doubling time before current date

Note: This parameter is only available if you do not check the box for first hospitalized case.

The number of days required for the number of infected individuals to double. Doubling rate is meant to apply as an infection growth rate without interventions.

To account for reduced contact and other public health interventions, modify the Social distancing input. The doubling time is directly related to R0 and drives the rate of new cases during the early phases of the outbreak.

The American Hospital Association (AHA) initially projected a doubling time between 7 and 10 days. The doubling time is applied to the number of infections, not the number of confirmed cases. This distinction may explain the discrepancy between the AHA's doubling time estimates and the observed doubling time of confirmed cases (currently 2 - 4 days).

Social distancing (% reduction in social contact)

The estimate of how much social contact is reduced in your region compared to no social distancing at all.

This parameter allows users to explore how reduction in transmission via policies (e.g. school closures or remote work) or other methods (e.g. hand-washing, increased disinfection of surfaces) might slow the rate of new infections.

See our blog post for more information, and estimates of effects of social distancing in Ferguson et al.

Severity Parameters

Hospitalization %(total infections)

The percentage of all infected cases which will need hospitalization.

This percentage, along with the number of Hospitalized COVID-19 Patients, and the Hospital Market Share (%) inform the Estimated # of Currently Infected Individuals measure.

See Verity et al. which suggests that around 5% of infected people need hospitalization, while also supplying an age adjustment methodology should you want to calibrate it to your own population.

Note: There is a large amount of uncertainty surrounding this figure as hospitalization requirements might vary between regions.

ICU %(total infections)

The percentage of all infected cases which will need to be treated in an ICU.

Similarly referenced by Verity et al. and assumed to be about 30% of admissions. Note the uncertainty due to treatment variation between regions.

Ventilated %(total infections)

The percentage of all infected cases which will need mechanical ventilation.

Similarly referenced by Verity et al. and assumed to be about 30% of admissions. Note the uncertainty due to treatment variation between regions.

Infectious days

The number of days a person can infect another person (regardless of whether the infected person symptomatic or asymptomatic).

This represents gamma (γ) in the SIR model.

Length of Stay

We present three different Length of Stay (LOS) metrics which we treat as self contained (independent). These LOS metrics are not additive; Do not sum the three parameters below.

Average Hospital Length of Stay (days)

The average number of days a COVID-19 patient is in the hospital.

This is inclusive of all hospitalized COVID-19 patients, regardless of the highest level of care they receive.

The default value is based on observed full hospital length of stay for ~10,000 Respiratory Failure patients at four Penn Medicine facilities over a 5 year period. We used internal data over COVID-19-treated patients from other countries due to lack of clarity over differing treatment protocols.

Average Days in ICU

The average number of days a COVID-19 patient is in the ICU.

This includes both vented and non-vented patients.

The default value of 9 days is based on observed full hospital length of stay for ~4,000 Respiratory Failure patients at four Penn Medicine facilities over a 5 year period requiring ICU support. We used internal data over COVID-19-treated patients from other countries due to lack of clarity over differing treatment protocols.

Average Days on Ventilator

The average number of days a COVID-19 patient is on mechanical ventilation.

The default value of 10 days is based on observed full hospital length of stay for ~2,000 Respiratory Failure patients at four Penn Medicine facilities over a 5 year period requiring ventilation support. We used internal data over COVID-19-treated patients from other countries due to lack of clarity over differing treatment protocols.

Display Parameters

Number of days to project

The number of days to show on the x-axis of the graphs. The max number of days is set to 30, as the model should be used to predict only a few weeks into the future.

Note: If the peak happens after the last projected day, the reported numbers for peak data will be inaccurate. In that case, increase the number of days to project in order to see the true peak.

Set the Y-axis on graphs to a static value (Checkbox)

Use this checkbox to set the y-axis of the graphs to a static value.

By default, the y-axis automatically scales based on the peak value of the projections.

Current date

The date in Year/Month/Day format to represent when projections are calculated.

A vertical line is displayed in the graphs at this date to provide context of time.

The default is today's date. Earlier dates can be used if the latest known data is not from today, or to re-run past reports with the current model.

Additional references

For a listing of additional references to help select parameter inputs, see the excellent MIDAS compilation