Inclusion, characteristics and credibility of systematic reviews in doctoral theses: A cross-sectional study of all Medical Faculties in Sweden

Objective Systematic reviews (SRs) are essential to ensure that decisions are informed by an up-to-date and complete understanding of the relevant research evidence. Conducting SRs within a doctoral thesis can reduce redundant, harmful and unethical research, identify knowledge gaps, and help the doctoral student obtain important skills to conduct and use research. The output and learning process of SRs overlaps with the aims of doctoral programs. We aim to explore to what extent SRs are included in doctoral theses from all medical faculties in Sweden, and to describe the type, topic and assess the credibility of the reviews. Study design and setting Duplicate assessors independently searched local and national repositories for doctoral theses published in 2021 within all seven medical faculties in Sweden, and categorized identified reviews based on review type, topic, and credibility using AMSTAR-2. Results 5.4% (45/852) of all doctoral theses included a review, and 1.3% (45/3461) of all included studies were reviews. Of these, two thirds (31) were SRs and the rest (14) were broader ‘big picture’ reviews. The most common topics were interventions (42%) and exposure/etiology (32%), with no reviews of diagnostic tests. The majority of the SRs had very low (71%) or low (19%) credibility, and few reached a high (7%) or moderate (3%) credibility. The most common issues were limitations with protocols, limited search strategies, and failure to account for risk of bias in drawn conclusions. Conclusions Few doctoral students included SRs in their theses, and the few SRs included in doctoral theses generally had a low credibility. Increasing the rate and quality of SRs in doctoral theses can help improve quality and relevance of subsequent primary research, and help students develop important skills. Actions are needed to support doctoral students to conduct high quality SRs. What is new? Few doctoral students included systematic reviews (SRs) in their theses The few SRs included in doctoral theses generally had a low credibility Increasing the rate of SRs can help improve the relevance of subsequent research Moreover, to support development of important skills and reach educational goals Actions are needed to support doctoral students to conduct high quality SRs