The phrase "a study that showed" is correct and usable in written English.
You can use it when referring to research findings or results from a specific study.
Example: "A study that showed the effectiveness of the new drug was published last month."
Alternatives: "a study indicating" or "research demonstrating".
The General Accounting Office has published a study that showed we could save $67 billion a year by adopting the Canadian system.
In 2009, British psychology researchers reported the results of a study that showed swearing altered pain perception.
I did a study that showed that evaluations are just as accurate if you did them within 48 hours.
Recently, I read about a study that showed a multi-strain probiotic interfered with the microbiome returning to normal.
The International Energy Agency released a study that showed renewable energy actually lost ground, as a percentage of the total supply of power, from 1970 to 2001.
The F.D.A. asked the company for a study that showed the drug was not inferior to other treatments for severe psoriasis.
Soon, he was sure, there would be a study that showed that the mentally ill were actually better-looking than other people.
The Insurance Institute recently completed a study that showed fatal crashes involving drivers 70 and older have substantially declined in this decade.
I once heard of a study that showed people who keep all their teeth live an average of ten years longer than those who don't….ten years!
I did a study that showed you had much less recidivism if you didn't put people in the stockade for their first AWOL, but gave them company punishment.
Stanford researchers conducted a study that showed women who mastered skills for maintaining their weight before they began a diet were better able to avoid regaining the weight.
