The phrase "are a bigger source" is correct and usable in written English.
It can be used when comparing the size or significance of different sources of information, resources, or influences.
Example: "These new studies indicate that social media platforms are a bigger source of misinformation than traditional news outlets."
Alternatives: "constitute a larger source" or "represent a greater source".
Farmers' fields are a bigger source of water contamination in China than factory effluent, the Chinese government revealed today in its first census on pollution.
Mr. Simon reports that Zion's Christian soldiers say they are a bigger source of support for Israel than American Jews, a notion Mr. Wieseltier calls "insulting to the American Jewish community".
About 3 billion of the Earth's inhabitants get a fifth or more of their protein from fish which means that fish are a bigger source of the stuff than beef is.The difficulty is, in part, a consequence of the problem known as the tragedy of the commons, whereby a commonly held resource is over-exploited.
Tax refunds are a big source of spending for consumers who could not afford bigger-ticket items during the holiday shopping season.
These are a big source of corruption: some businesses get two or three inspections daily.
More provisioning reduces the Bank's profits, which are a big source of cash for the poorest developing countries.
And the Jeep Grand Cherokee S.U.V.'s produced there are a big source of overall corporate profits.
The chancellor's problem is that business rates are a big source of revenue, bringing in £26.5bn last year.
Although personal computers are a big source of revenue for the company, they are a low-margin business, about 6.4 percent in the latest quarter.
Marketmakers say a ban would make it harder for them to offset risks, since speculative buyers are a big source of liquidity.
One reason is that the state owns most natural resources and banks; these are a big source of crony wealth in other emerging economies.
