A 2017 study of Switzerland found that naturalization strongly improves long-term social integration of immigrants: "The integration returns to naturalization are larger for more marginalized immigrant groups and when naturalization occurs earlier, rather than later in the residency period." A separate study of Switzerland found that naturalization improved the economic integration of immigrants: "winning Swiss citizenship in the referendum increased annual earnings by an average of approximately 5,000 U.S. dollars over the subsequent 15 years. This effect is concentrated among more marginalized immigrants."