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Increasingly there are large amounts of digital data that can be harnessed for epidemiological research. The theme of this thesis is to describe how digital data, in particular electronic health records (EHR) and data collected through an online health community, can be used to answer questions about the management of rheumatoid arthritis (RA). These two data sources have different strengths - EHRs produce large longitudinal datasets representing the whole of the UK and can be linked to other administrative datasets. For bespoke surveys, collecting data through an online health community is a quick and efficient method to identify issues important to patients. Both have limitations that need addressing through careful use of epidemiological techniques. This thesis presents seven studies that highlight these methodological challenges focused on two interventions used to manage RA: vaccinations and glucocorticoids. Primary care EHR data was used to estimate influenza and pneumococcal vaccination uptake the UK (publication 1) and timing of pneumococcal vaccination in relation to starting disease-modifying anti-rheumatic drugs (publication 2), where the main challenges addressed were related to misclassification. EHR data was used to answer questions related to adverse outcomes associated with glucocorticoids: mortality, overall (publication 3) and in people with comorbid type 2 diabetes mellitus (publication 4), and hypertension (publication 5). These studies required careful preparation of drug data to correctly attribute risk and consideration of biases such as peri-mortal bias and surveillance bias. Data collected through an online health community measured patient perspectives of glucocorticoid side effects (publication 6) and the challenge of representativeness of responders was directly addressed through capturing the characteristics of patients with RA and comparing them to patients with RA identified using EHR data to understand the representativeness of online health community responders (publication 7). The studies highlighted important clinical issues: 1) vaccination uptake was not occurring as guidelines recommend, 2) glucocorticoid use was associated with increased risk of mortality and hypertension, 3) the glucocorticoid side effects of importance to patients are not frequently researched and 4) patients recruited through online health communities represent a younger and more diverse RA population. The thesis shows how digital data can be used, to successfully address a variety of previously unanswered questions, related to different aspects of RA management, using methods applicable to the investigation of other chronic diseases.