This supplementary appendix provides additional information for the study "Prospective memory assessment before and after Covid-19" by Ellingjord-Dale M, Brunvoll SH, Søraas A, et al., published in the New England Journal of Medicine in 2024. The appendix includes detailed methods, statistical analyses, and sensitivity analyses to support the main findings. **Methods:** - **Study Design and Subjects:** The Norwegian Covid-19 Cohort Study is a population-based, open cohort study of participants aged 18-96 years. The study aimed to identify risk factors and examine the routes of SARS-CoV-2 infection. Participants were recruited through social media and nationwide media coverage, with most included within the first month of the study. - **Questionnaires:** The Everyday Memory Questionnaire (EMQ) was used to assess memory problems. The EMQ scores were averaged over all items, not the total sum. - **SARS-CoV-2 Testing:** Testing was conducted according to official Norwegian guidelines, initially using RT-PCR and later including self-testing. - **Statistical Analyses:** A linear mixed effects model was used to estimate mean EMQ scores and 95% confidence intervals, adjusting for various covariates such as age, sex, BMI, income, smoking status, underlying medical conditions, and questionnaire number. **Limitations:** - The study had a lower response rate for the second EMQ questionnaire, which could introduce response bias. - Self-reporting in the EMQ questionnaires may lead to information or recall bias. **Sensitivity Analyses:** - Additional analyses were conducted to account for missing data and to explore the impact of different covariates on EMQ scores. The appendix also includes detailed tables and figures that provide frequency distributions, mean values, and confidence intervals for various analyses, as well as sensitivity analyses to validate the findings.This supplementary appendix provides additional information for the study "Prospective memory assessment before and after Covid-19" by Ellingjord-Dale M, Brunvoll SH, Søraas A, et al., published in the New England Journal of Medicine in 2024. The appendix includes detailed methods, statistical analyses, and sensitivity analyses to support the main findings. **Methods:** - **Study Design and Subjects:** The Norwegian Covid-19 Cohort Study is a population-based, open cohort study of participants aged 18-96 years. The study aimed to identify risk factors and examine the routes of SARS-CoV-2 infection. Participants were recruited through social media and nationwide media coverage, with most included within the first month of the study. - **Questionnaires:** The Everyday Memory Questionnaire (EMQ) was used to assess memory problems. The EMQ scores were averaged over all items, not the total sum. - **SARS-CoV-2 Testing:** Testing was conducted according to official Norwegian guidelines, initially using RT-PCR and later including self-testing. - **Statistical Analyses:** A linear mixed effects model was used to estimate mean EMQ scores and 95% confidence intervals, adjusting for various covariates such as age, sex, BMI, income, smoking status, underlying medical conditions, and questionnaire number. **Limitations:** - The study had a lower response rate for the second EMQ questionnaire, which could introduce response bias. - Self-reporting in the EMQ questionnaires may lead to information or recall bias. **Sensitivity Analyses:** - Additional analyses were conducted to account for missing data and to explore the impact of different covariates on EMQ scores. The appendix also includes detailed tables and figures that provide frequency distributions, mean values, and confidence intervals for various analyses, as well as sensitivity analyses to validate the findings.