The EGM reveals two major types of evidence gaps in the literature: ‘absolute’ gaps, where no or few primary studies have been conducted, and ‘synthesis’ gaps, where no SR exists despite a cluster of IEs or the quality of the SRs is substandard or the existing SRs are dated. The major gaps are presented below.

# 3.1.1 The geographic and economic context

The evidence base is skewed towards high-income and Western countries with more limited evidence from low- and middle-income countries (LMICs). In terms of location, there is limited evidence from the WHO regions of Africa, South-East Asia, and Eastern Mediterranean as most of the studies (66%) were conducted in the two regions of America and Europe. Similarly, very few studies were conducted in LMICs and there exists a huge gap in the volume of studies conducted in rich and poor countries. For instance, over three-quarters of the studies were conducted in high-income countries, with the United States alone contributing one-third of the included IE studies.

# 3.1.2 The intervention coverage

The intervention framework comprises four DHI categories divided further into 28 specific types of DHIs. Across the four intervention categories, almost all studies evaluated interventions for clients and health care providers. Significant evidence gaps were found for the other two categories, which were together covered by five studies only. See Figure 3 for a survey of coverage.

Notwithstanding the large volume of IEs covering clients and providers’ DHIs, the evidence base within these intervention categories is unevenly distributed. For example, there is a limited literature on DHIs that empower clients to take the lead on health issues affecting them through, for example, citizen reporting or client-client communication. The focus for most studies is largely on top-down or externally led interventions such as targeted communication interventions. For the health care providers, there is a heavy focus on DHIs concerned with service delivery (e.g., telemedicine or decision support). Interventions that support providers in planning or coordination of health services (e.g., referral or activity scheduling) have received relatively low attention. There is limited evidence of DHIs for health system or resource managers and data services.

# 3.1.3 Frequency of AI use

Despite the potential role of AI in strengthening health systems and improving the quality of health care, a shallow evidence base was found in the published literature for AI. The number of studies that evaluated AI-powered interventions is extremely low. In total, only 13% (n=83) of the studies covered interventions that incorporated AI. Possible reasons include slow adoption of AI in the health sector, limited use of peer-reviewed publications as a mechanism of measuring impact, or a long and rigorous vetting processes that may be required in the medical field. This could also be due to the inclusion criteria of the EGM, which was focused on IEs that utilize counterfactual analysis. This may not be a common approach in AI-related evaluations.

# 3.1.4 Health domains

Not many studies covered critical global health domains such as maternal health, nutrition, HIV/AIDS, and family planning/reproductive health. No more than 45 studies covered each of these domains compared to the 343 studies that covered NCDs. While the majority of IEs were concerned with NCDs, there is also a substantial focus on mental health, infectious