Why do per capita COVID-19 Case Rates Differ Between U.S. States?

  1. Lloyd Chambless

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Abstract

Background

The popular press has explored the differences among U.S. states in rates of COVID-19 cases, mostly focusing on political party differences, and often mentioning that political party differences in health outcomes are confounded by demographic and socio-economic differences between Democratic areas and Republican areas. The purpose of this paper is to present a thorough analysis of these issues.

Design and Methods

State-specific COVID-19 cases per 100,000 people was the main outcome studied, with explanatory variables from Bureau of Census surveys, including percentages of the state population that were Hispanic, black, below poverty level, had at least a bachelor’s degree, or were uninsured, along with median age, median income, population density, and degree of urbanization. We also included political party in power as an explanatory variable in multiple linear regression. The units of analysis in this study are the 50 U.S. states.

Results

All explanatory variables were at least marginally statistically significantly associated with case rate in univariate regression analysis, except for population density and urbanization. All the census characteristics were at least marginally associated with party in power in one factor analysis of variance, except for percentage black. In a forward stepwise procedure in a multivariable model for case rate, percentages of the state population that were Hispanic or black, median age, median income, population density, and (residual) percentage poverty were retained as statistically significant and explained 62% of the variation between states in case rates. In a model with political party in power included, along with any additional variables that notably affected the adjusted association between party in power and case rate, 69% of the variance between states in case rates was explained, and adjusted case rates per 100,000 people were 2155 for states with Democratic governments, 2269 for states with mixed governments, and 2738 for Republican-led states. These estimates are based on data through October 8, 2020.

Conclusions

U.S. state-specific demographic and socio-economic variables are strongly associated with the states’ COVID-19 case rates, so must be considered in analysis of variation in case rates between the states. Adjusting for these factors, states with Democrats as the party in power have lower case rates than Republican-led states.

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  1. ScreenIT

    SciScore for 10.1101/2020.10.16.20213892: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board Statementnot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    The Times has compiled this data from state and local governments and health departments.
    Times
    suggested: (Lab Times, RRID:SCR_000657)

    Results from OddPub: Thank you for sharing your data.

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    There are clearly weaknesses in the COVID-19 case data now available. Foremost in the U.S. is the variability among the states in the frequency, timing, and priorities of testing for the virus. There may also be variation in test reliability and in completeness of data collection. We analyze rates of confirmed or probable cases and not the rates of Covid-19 infection. Actual counts of infections will never be available, though estimates of infection rates through antibody testing may be. Rates of hospitalization for COVID-19 would be an alternative disease measure to consider, but 14 states do not offer such data. The results of our analysis of COVID-19 death rates were inconclusive. There are several potential reasons for this. First, the numbers of deaths are far fewer than those for cases. Second, when enough time has elapsed to ascertain vital status of COVID-19 cases, COVID-19 death rates are a product of case rates times case fatality, where case fatality is the probability of death from COVID-19 among COVID-19 cases. Socio-economic and demographic factors and state public health policies could have different effects on these two components of COVID-19 death rates. Third, there may be additional variation in how “confirmed or probable COVID-19 death” is defined. Fourth, COVID-19 death rates may be changing over time.27 Some investigators have found that there is no evidence that age-specific COVID-19 case fatality is changing over time,28,29 but changes in the age distr...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. Version published to 10.1101/2020.10.16.20213892 on medRxiv