"improper method" is correct and usable in written English.
Example sentence: The engineer was reprimanded for using an improper method to fix the broken machine.
The Metro evidently concluded that the ads would offend Catholics, since the church teaches that vasectomies are an improper method of birth control.
As it turned out, the appraiser Mr. Percudani used most often, Dominick Stranieri, surrendered his license in 2002 to settle an unrelated case in which the state alleged that he overvalued homes by using an improper method.
Major shortcomings were included, such as improper method of randomization and concealment of allocation, analysis not based on the intention-to-treat principle, and especially unsystematic and insufficient reporting of studies.
3. Using improper methods to exclude papers from journals or from reports by the Intergovernmental Panel on Climate Change (IPCC).
A blood facility in Philadelphia, with approval from a senior national executive, decided not to recall some 600 units of blood that had been collected using improper methods.
But AOL blocked the new systems, which were introduced in the summer of 1999, contending that they used improper methods to gain access to its system.
It is as much his duty to refrain from improper methods calculated to produce a wrongful conviction as it is to use every legitimate means to bring about a just one".
The team discovered that the facility, with the approval of a senior executive at the national headquarters in Washington, had decided not to recall some 600 units of blood collected using improper methods.
After revelations last fall that several major banks had used improper methods to speed foreclosures, the courts are increasingly becoming a central battleground for people seeking to modify their loan and salvage their house.
"Judicial practice in recent years shows that slack and improper methods have been used to gather, examine and exclude evidence in various cases, especially those involving the death penalty," said a statement released by the central government.
There's no evidence (yet, anyway) that state-sponsored accounts used "improper methods" to boost search rankings, though anyone who's seen fake news featured high up in their search results might rightfully have questions about how the company decides what flies in search and what doesn't.
