Table 1 Variables used in the analysis

1

Type of collaboration^a

If a study involved at least one country in the South and at least one country in the North then type of collaboration is N–S (coded 1), else South-South (coded 0). Type of collaboration was derived from data about “Sponsor/Collaborators” and “Locations”

2

Principal investigators

A dichotomous variable indicating whether the study involved a single principal investigator ([PI], or Study Director, or Chair) (coded 0) or multiple PIs (coded 1)

3

Size of collaboration (Number of Institutions)^a

A continuous variable indicating number of institutions involved in the collaboration. This variable was categorized into: 3 + institutions (coded 2) vs. 2 institutions (coded 1) vs. 1 institution (coded 0). This variable was derived from data about “Sponsor/Collaborators” and “Locations”

4

Study location^a

A continuous variable indicating total number of study locations. This variable was categorized into: 3 + locations (coded 2) vs. 2 locations (coded 1) vs. a single location (coded 0)

5

Study size

A continuous variable indicating total number of participants enrolled in the study. This variable was derived from data about “Enrollment.” Study size was categorized into large (100 + participants—coded 2) vs. medium (50–99 participants—coded 1) vs. small size (< 50 participants—coded 0)

6

Funding source

A categorical variable describing the organization that provides funding or support (e.g., for activities related to study design, implementation, data analysis, and reporting) for a clinical study. According to ClinicalTrials.gov, organizations listed as sponsors and collaborators are considered the funders of the study. Whereas the database has four types of funders (U.S. NIH; other US Federal agencies; Industry; and All Others), these were re-coded as follows: public-funded including U.S. NIH and other federal agencies (coded 0), industry-funded such as pharmaceutical and device companies (coded 1), jointly funded by public and industry (coded 2), or Other including individuals, universities, community-based organizations, (coded 3). This variable was derived from data about “Sponsor/Collaborators”

7

Study design

A dichotomous variable indicating whether a trial was interventional (coded 1) or observational study (coded 0). Briefly, an interventional study is whereby the investigator assigns participants to groups that receive one or more interventions (or no intervention) so that effects of the interventions on biomedical or health-related outcomes can be evaluated whereas observational study is whereby there is no assignment of participants to a specific intervention, rather participants are identified as belonging to study groups and are assessed for biomedical or health outcomes

8

Gender

A categorical variable indicating participants’ self-representation of gender identity. Gender was coded 0 if a study include males only, 1 if it includes females only, and 2 if it includes a mixture of males and females

9

Age

A categorical variable indicating study participants’ age group. Age was coded 0 if study include only adults (age 18 and above), 1 if it includes only children (age 17 or below), and 2 if it includes a mixture of adults and children

10

Study duration (in years)^a

A continuous variable indicating the number years taken from start to completion of the study. To compute study duration, we subtracted “Study Start Date” (i.e., the actual date on which the first participant was enrolled in a clinical study) from “Study Completion Date” (i.e., the date on which the last participant was examined or received an intervention). Study duration was categorized into long (coded 2) vs. medium (coded 1) vs short (coded 0). If data on “Study Completion Date” were missing, then “Primary Completion Date” was used and if this was also missing, then date “Last Verified” was used. If only month and year were recorded, then the first day of the month was entered