O que significa strong overarching pattern ?

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Historically, strong labor unions have been integral to a vibrant middle class. Collective bargaining has helped improve wages, benefits, and rights for workers, both union and nonunion alike, nationwide. However, according to the Economic Policy Institute, a nonpartisan think tank, union membership has fallen considerably in the last several decades. In addition to declining membership, labor laws have weakened unions and their ability to contribute to higher wages. Since union membership began to rapidly decline in the 1980s, the share of income going to the top 10% of earners has increased dramatically.

Perhaps because unions are not as influential as they once were, there does not appear to be a strong overarching pattern between union membership and stagnant middle class wages. Nationwide, some 11.1% of all working adults are union members. Among the states where the middle class is disappearing, unionized workers comprise anywhere from 5.2% of workers in Arizona to 24.7% in New York.