Nearly eight years ago, Hauke Hillebrandt wrote the following:

Sometimes people ask us about the effectiveness of donating to Amnesty International, Human Rights Watch, Global Financial Integrity, Tax Justice, or Transparency International - these all seem like organisations that could potentially be very effective, but we don’t currently even have a good idea about their relative strengths and weaknesses, how they would spend additional money, if they work in areas of the advocacy space that are not already very crowded, and if they are working on causes that at least appear tractable.

About three years ago, Hillebrandt and John G. Halstead wrote a popular essay where they argue, in effect, that effective altruism neglects interventions that could contribute to economic growth in low-income countries. Such interventions, I imagine, would at least partially be through advocacy organizations whose impact cannot easily be measured using randomized controlled trials. Indeed, Hillebrandt and Halstead suggested that "research and advocacy for growth-friendly economic policies can often be orders of magnitude more cost-effective than direct funding of evidence-based interventions."

In animal welfare and existential risk, advocacy is often the best or only intervention. This is not the case in global health and development, at least in the short-term. However, this does not necessarily mean that there are no cost-effective advocacy organizations working in this cause area which effective altruists should support. I am personally even interested in donating to such charities. So my question is: what are some policy advocacy organizations working in global health and development that seem (potentially) cost-effective?

Thank you in advance for your reply and for the high quality of the responses I get on this forum.