The phrase "are a substantial part" is correct and usable in written English.
It can be used when discussing the significance or importance of a particular element within a larger context.
Example: "The environmental factors are a substantial part of the overall success of the project."
Alternatives: "constitute a significant portion" or "represent a major component".
Marble quarries are a substantial part of Dorset's history.
"With projected ridership of over 36 million by 2018, ferry services are a substantial part of the transit mix in New York," said Roland Lewis of the Metropolitan Waterfront Alliance, a pro-ferry non-governmental organisation.
These events are a substantial part of the tower's annual income and, without a grand gesture from the companies involved, there is no way to avoid taking down the bulk of the installation next week.
Because elderly patients are a substantial part of the oncology population, their types of treatment as well as the possible impact their treatment will have on healthcare resources need to be further examined.
Although the productivity costs are a substantial part of the total cost, it has a relatively small impact on the bootstrapped ICERs.
Adverse effects and pregnancy represent the two most common categories of questions to RELIS and are a substantial part of the QAP database.
The carriers are now realizing that wireless data is a substantial part of the business".
"That is not suggestive that terrestrial foods could be a substantial part of their diet".
In a veiled criticism of Congress, Mr. Fox said, "Freedom of dissent is a substantial part of any democracy, but willful dissent is merely a display of intransigence".
Online shopping is a substantial part of consumer spending, representing £21 in every £100 spent on cards at UK retailers – the first time the figure has been collected.
Secondary buyouts, or transactions in which a private equity group buys a business from another, have been a substantial part of leveraged buyout activity this year.
