Summary of variable selection for unweighted and weighted modelling of having received or planning to receive COVID-19 vaccination using an adaptive lasso approach*
| Covariates | Unweighted | Weighted | ||
| Estimated coefficient | P value | Estimated coefficient | P value | |
| Age ≥60 | 0.29 | 0.12 | 0.78 | <0.001 |
| Race: Other | – | – | 0.08 | 0.68 |
| What is the highest education you have achieved? Beyond 4-year college degree | 0.80 | <0.001 | 0.67 | <0.001 |
| Number of children/minors under 18 in your household None | 0.35 | 0.01 | 0.13 | 0.27 |
| Region: Midwest | – | – | 0.44 | <0.001 |
| Log (number of close friends) | 0.98 | <0.001 | 1.35 | <0.001 |
| Has a doctor or nurse ever told you that you have post-traumatic stress disorder? No | – | – | 0.83 | <0.001 |
| Has a doctor or nurse ever told you that you have alcohol use disorder? Yes | – | – | 1.15 | <0.001 |
| Has anyone close to you (eg, family, friend) tested positive for COVID-19? No | – | – | 0.47 | <0.001 |
| In the past 3 months (ie, since 1 November 2020), have you tested positive for COVID-19? Yes, positive test result | 0.81 | 0.09 | – | – |
| How much of a threat do you view the COVID-19 virus on Americans? Great threat | 0.95 | <0.001 | 0.93 | <0.001 |
| What is your opinion of the government’s response to COVID-19? Great under-reaction | – | – | 0.75 | <0.001 |
| In the past 3 months, how often did you wear masks when you were in public? Always | 1.38 | <0.001 | 1.18 | <0.001 |
| How much would you rate that any of the above mental health symptoms you reported are related to COVID-19? Great amount | 0.52 | 0.03 | – | – |
| ‘I'm worried that the COVID-19 vaccine isn't safe.’ No | 2.25 | <0.001 | 2.07 | <0.001 |
| ‘I feel that I’m not at-risk for COVID-19 and so don’t need the vaccine.’ No | 1.67 | <0.001 | 1.47 | <0.001 |
| ‘I have already had COVID-19 so I don’t believe vaccine is necessary.’ No | 1.42 | <0.001 | 2.35 | <0.001 |
| ‘I don’t have any concerns about getting the COVID-19 vaccine.’ Yes | – | – | 1.10 | <0.001 |
| ‘Other reason’ No | 1.59 | <0.001 | 1.79 | <0.001 |
| AUC | 0.92 | 0.92 | ||
*P values and estimated coefficients are obtained by refitting the logistic model with variables selected by the adaptive lasso.
AUC, area under the curve; lasso, least absolute shrinkage and selection operator.