"usually a combination of" is correct and can be used in written English.
It is typically used when describing something that is made up of multiple elements or factors. For example: - The success of a business is usually a combination of a good product, effective marketing, and strong leadership. - The flavor of this dish is usually a combination of sweet and savory ingredients. - The outcome of a soccer game is usually a combination of individual skill and team strategy. - The cause of a disease is usually a combination of genetic predisposition and environmental factors.
"It's usually a combination of both for me," says Clarke.
It has a short coat, which is usually a combination of black, tan, and white.
The motorcycle frame is often of steel, usually a combination of tubes and sheets.
The treatment for older adults with ADHD is similar to the protocol for children with the disorder – usually a combination of "pills and skills", according to Goodman.
Most diehard smokers need methods far stronger — and usually a combination of stop-smoking aids — to help quit in the first place and, more important, remain former smokers.
It looks like a small foxhound and has large brown eyes, hanging ears, and a short coat, usually a combination of black, tan, and white.
Ms. Hubley's solo films, usually a combination of her watercolor paintings and cel animation, often dealt in a poetic way with the treatment of women ("Witch Madness," 1999) and with pre-Christian myths.
(Much as we would like to explain clinical depression by making it either genetics or environment, bad wiring or bad nurturing, it is usually a combination of the two that sets the illness off).
This state is seen more often in ectothermic animals than in endotherms, but in both the stimulus for estivation is usually a combination of high temperatures and water shortage.
First off, there's the stuff used to season the beans – usually a combination of salted meats, such as hunks of pancetta, bacon or cured pork belly, and fat and gelatine represented by pork rind and trotter, as used by Olney, Hugh Fearnley-Whittingstall, Wolfert and Luard.
When they arrived, finding no homes or land at prices they could afford, they squatted on unused land on the sides of the mountains, and began to surround the city with their own makeshift dwellings, built with whatever materials they could lay their hands on: usually a combination of brick, breeze block and tin, or for the less fortunate, cardboard.
