• Source name: hospital-admissions
• Earliest issue available: June 21, 2020
• Number of data revisions since May 19, 2020: 1
• Date of last change: October 20, 2020
• Available for: county, hrr, msa, state (see geography coding docs)
• Time type: day (see date format docs)

## Overview

This data source is based on electronic medical records and claims data about hospital admissions, provided to us by health system partners. We use this inpatient data to estimate the percentage of new hospital admissions with a COVID-associated diagnosis code in a given location, on a given day.

Signal Description
smoothed_covid19_from_claims Estimated percentage of new hospital admissions with COVID-associated diagnoses, based on claims data from health system partners, smoothed in time using a Gaussian linear smoother
Earliest date available: 2020-02-01
smoothed_adj_covid19_from_claims Same as smoothed_covid19_from_claims, but with systematic day-of-week effects removed using the same mechanism as in doctor-visits
Earliest date available: 2020-02-01
smoothed_covid19 Estimated percentage of new hospital admissions with COVID-associated diagnoses, based on electronic medical record and claims data from health system partners, smoothed in time using a Gaussian linear smoother. This signal is no longer updated as of 1 October, 2020.
Earliest date available: 2020-02-01
smoothed_adj_covid19 Same as smoothed_covid19, but with systematic day-of-week effects removed using the same mechanism as in doctor-visits. This signal is no longer updated as of 1 October, 2020.
Earliest date available: 2020-02-01

## Lag and Backfill

Hospitalizations are reported and processed by the health system partners several days after they occur, so the signal is typically available within several days of lag. This means that estimates for a specific day are only available several days later.

The amount of lag in reporting can vary, particularly whether the data comes from electronic medical records or from processed claims. After we first report estimates for a specific date, further hospitalization data may arrive for that date, or diagnoses for admissions from that date may change. When this occurs, we issue new estimates. This means that a reported estimate for, say, June 10th may first be available in the API on June 14th and subsequently revised on June 16th.

As claims and records are available at a significant and variable latency, the signal experiences heavy backfill with data delayed for a couple of weeks. We expect estimates available for the most recent 7-13 days to change substantially in later data revisions (having a median delta of 10% or more). Estimates for dates more than 57 days in the past are expected to remain fairly static (having a median delta of 1% or less), as most major revisions have already occurred.

## Limitations

This data source is based on electronic medical records and claims data provided to us by health system partners. The partners can report on a portion of hospitalizations, but not all of them, and so this source only represents those hospitalizations known to them. Their coverage may vary across the United States.

We receive two daily data streams of new hospital admissions recorded by the health system partners at each location. One stream is based on electronic medical records, and the other comes from claims records.

In the electronic medical records stream, admissions are considered COVID-associated if they meet the following criteria:

• If the admission has any ICD-10 code matching {U071, U072, B9729}, or
• If the primary ICD-10 code is one of {R05, R060, R509, Z9911, R0902, R0603, R0609, R062, R069, R0602, R05, R0600, J9691, J9692, J9621, J9690, J9601, J9600, J189, J22, J1289, J129, J1281, B9721, B9732, B342, B349, A419, R531, R6889} and there is a secondary ICD-10 code of Z20828, or
• If the primary ICD-10 code is Z20828.

For the claims stream, admissions are considered COVID-associated if the patient has a primary ICD-10 code matching {U071, U072, B9729, J1281, Z03818, B342, J1289}.

## Estimation

For a fixed location $$i$$ and time $$t$$, let $$Y_{it}$$ denote the number of hospital admissions meeting the qualifying conditions. Let $$N_{it}$$ denote the total number of hospital admissions.

Our estimate of the COVID-19 percentage is given by

$\hat p_{it} = 100 \cdot \frac{Y_{it} + 0.5}{N_{it} + 1}.$

The additional pseudo-observation of 0.5 means this estimate can be interpreted as the posterior mode of a binomial proportion with a $$\text{Beta}(1/2, 1/2)$$ Jeffreys prior. The practical effect is to prevent $$\hat p_{it}$$ from being exactly zero or one, which would result in estimated standard errors of 0. The estimated standard error is:

$\widehat{\text{se}}(\hat{p}_{it}) = 100 \sqrt{\frac{\frac{\hat{p}_{it}}{100}(1-\frac{\hat{p}_{it}}{100})}{N_{it}}}.$

### Data Streams

• smoothed_covid19 and smoothed_adj_covid19: This signal combines data from electronic medical records (emr) and claims records. Here, $$Y_{it} = Y_{it}^{\text{emr}} + Y_{it}^{\text{claims}}$$ is the number of hospital admissions meeting the qualifying conditions, where the superscript denotes the respective data stream. Similarly, $$N_{it} = N_{it}^{\text{emr}} + N_{it}^{\text{claims}}$$ is taken as the total number of hospital admissions. Thus, the estimate of the COVID-19 percentage is weighted by the contribution from each data stream according to the magnitude of their total admissions.
$\hat p_{it} = 100 \cdot \frac{Y_{it} + 0.5}{N_{it} + 1} \approx 100\cdot\left(\frac{N_{it}^{\text{emr}}}{N_{it}}\cdot\frac{Y_{it}^{\text{emr}}}{N_{it}^{\text{emr}}} + \frac{N_{it}^{\text{claims}}}{N_{it}}\cdot\frac{Y_{it}^{\text{claims}}}{N_{it}^{\text{claims}}} \right)$
• smoothed_covid19_from_claims and smoothed_adj_covid19_from_claims: This signal uses data solely from the claims stream: $$Y_{it} = Y_{it}^{\text{claims}}$$ and $$N_{it} = N_{it}^{\text{claims}}$$.

This source undergoes the same backwards padding adjustment as the doctor-visits source; see its documentation.
This source undergoes the same smoothing adjustment as the doctor-visits source (see its documentation), with the exception that the smoothing is performed on the raw counts, rather than the raw rate.