# **1 Introduction**

The use of randomized control trials (RCTs) in the social sciences has greatly expanded over the past two decades, from economics and political science to public health and education.<sup>1</sup> In parallel, journals, funders, policy organizations, and organizations promoting open science have emphasized that original research data be publicly accessible for others to analyze and use. As a result of this concerted push, hundreds of original RCT datasets from a wide variety of contexts and populations are already published and in principle accessible to researchers, with the potential to benefit numerous areas of research.

However, there remain to date significant barriers to the discovery and use of existing RCT data. Published datasets are scattered across data repositories, journal and university websites, and researcher homepages. In many data repositories, filter options and documentation fields are broad, often consisting of free form text fields, and data quality and provenance are hard to assess. RCT data are often published with a focus on replicating the analysis in a specific paper, and the properties specific to RCTs and features of the data have to be pieced together from inspecting datasets, data appendices, and readme files. Combining datasets across studies is hindered by a lack of harmonization and documentation. Any work in this regard by individual researchers is lost to the next person who wants to conduct a similar study.

In this paper, we propose a metadata schema that can serve as the basis for a catalog of RCT data (or, more broadly, any social science experimental data). The metadata schema defines a set of fields with encoding schemes that can be used to describe datasets associated with social science experiments. The encoding scheme defines the acceptable formats and values to complete the field, such as free text entry, dates, numeric values, or controlled vocabularies (multiple choice options).<sup>2</sup> The proposal organizes fields into thematic modules and includes whether a field should be optional or mandatory. A core objective of this proposal is standardization. Standardizing the documentation of specific types of data allows harmonization, aggregation, and cross-referencing. Data repositories that follow a standardized schema can be easily made searchable by internet search engines such as Google Dataset Search. As much as possible, our schema therefore conforms with common data description standards (such as those of the Data Documentation Initiative (DDI)), and with existing schemata and catalogs for experiments as well as survey data from the social sciences (such as the World Bank’s Microdata Catalog, the AEA RCT Registry, and ClinicalTrials.gov).

In addition, we added fields that we considered particularly useful for secondary research. Datasets documented with the schema can be easily searched or filtered by many different criteria, from the type

> 1We use the term RCT to describe an experiment that uses randomization to assign some intervention or treatment to participants but is conducted outside of a controlled environment (such as a laboratory).

> 2We follow the definitions in ISO (2021).

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