There appears to be a marked difference between Democrat and Republican-dominated states concerning the fractions of the populations that are getting vaccinated (we obtain the vaccination rates from https://www.mayoclinic.org/coronavirus-covid-19/vaccine-tracker). One might expect this to be reflected in the confirmed COVID-19 cases. Therefore, we divided states into those Democrat-dominated and those Republican-dominated using the states that voted for Biden and the states that voted for Trump in the 2020 election as documented in https://en.wikipedia.org/wiki/Political_party_strength_in_U.S._states. We then scatter plotted the daily confirmed COVID-19 daily cases per million population (Mpop) for each US state for July 6, 2021 versus the % of each state's population that had one or more vaccine doses and also versus the % of each state's population that were fully vaccinated (2 shots of Pfizer or Moderna vaccine or 1 shot of Johnson & Johnson vaccine). The graphs for daily confirmed cases per Mpop for 7-6-2021 versus: the % of each state's population that had at least 1 dose; and for the % of each state's population that had completed their doses are shown below.
For the case of at least one dose we also identify many of the states by their 2 letter abbreviations (see https://www.infoplease.com/us/postal-information/state-abbreviations-and-state-postal-codes).
In both cases we show the Pearson linear correlations (see https://en.wikipedia.org/wiki/Pearson_correlation_coefficient) as dotted lines together with the equations for the lines and the correlation coefficients (R2)*.
Also looking at the residuals of (observed(daily confirmed cases per Mpop) - Pearson correlation prediction) versus % of population with at least one dose, we see:
The Democrat states have lower residuals (this results in a larger R2) with only one state (NV) with an absolute(residual) exceeding 40. The Republican states have 8 states (AR, MO, UT, FL, AL, ND, WV, SD) with an absolute residual exceeding 40.
For one dose: Democrat state populations are vaccinated 60.7% +- 6.8%, Republican states 46.6% +- 5.4%
As one goes from the % of the state's populations having received one vaccine dose to the % of the state's population having received all doses, the correlations (R2) of confirmed cases to doses increases from 25% to 31% for democrat states and from 5% to 14% for republican states.
The Democrat states have lower residuals between the observed daily confirmed cases per Mpop and that predicted by the trendline (this results in a larger R2) with only one state (NV) with an absolute(residual) exceeding 40. The Republican states have 8 states (AR, MO, UT, FL, AL, ND, WV, SD) with an absolute residual exceeding 40.
Plotting various demographics plotted versus the daily confirmed COVID-19 cases gives the following Pearson correlation coefficients R2 which expresses what fraction of the variability of your dependent variable (Y) is explained by your independent variable (X).
| Demographic (X) | R2 | slope |
| Income per capita | 17% | Negative |
| Median age | 6% | Negative |
| %Black+Hispanic+Asian | 2% | Positive |
| % Black+Hispanic | 3% | Positive |
| % Black | 1% | Positive |
| Pop density (pop/sq km) | 7% | Negative |
| % population fully vaccinated | 27% | Negative |
Conclusions
Increased vaccination rates lead to fewer confirmed cases.
Democrat states are doing much better than Republican states in vaccinating their populations.
The variability of confirmed daily cases per Mpop is much larger for Republican states than Democrat states. This appears to be, at least partially, a reflection of Democrat states having higher vaccination rates.
There are several demographics that appear to affect the confirmed cases. For example, the following demographics have a noticeable effect: %percent of population vaccinated 27%; Income per capita 17%; population density 7%; median age 6%. For all of these the lower the demographic the higher the confirmed cases.
For the Democratic states, roughly 25% of the reduction in daily confirmed cases is due to the increased % of the population with at least one COVID-19 vaccine shot.
As a result:
- All Republican states and a few Democrat states (Georgia (GA), Nevada (NV), and Arizona (AZ)), still have a way to go in vaccination rates before they see much improvement in daily COVID-19 confirmed cases.
Also see:
- https://covid.cdc.gov/covid-data-tracker/#county-view for a map of cases by county.
- The spreadsheet is available at https://www-iepm.slac.stanford.edu/pinger/covid/us-7-6-2021.xlsx
* We can use Pearson's R2 coefficient to evaluate the quality of fit of a model on data. It expresses what fraction of the variability of your dependent variable (Y) is explained by your independent variable (X).