"A multitude of studies" is correct and usable in written English.
You could use it in a sentence such as, "A multitude of studies have concluded that climate change is a real and pressing issue."
A multitude of studies have focussed on the connections between urban form, location and transport behavior to inform sustainable and resilient urban planning.
A multitude of studies has also illustrated its effects on the structure and function of the brain, especially in regions that govern rumination, "me-centered" thoughts, and anxiety.
A multitude of studies shows that telecommuters are more productive.
A multitude of studies have linked meditation with both physical and mental health benefits, from reduced depression and anxiety to improved immune system functioning.
A multitude of studies, data and anecdotal evidence supports the notion that optimists experience less stress, stronger immune systems and overall better health than their Debby Downer counterparts.
A multitude of studies have implicated alterations in the hypothalamo-pituitary-adrenal (HPA) axis in the vulnerability to develop stress-related disorders like major depression [1] [7].
A multitude of studies have identified various risk factors for ARTI.
A multitude of studies detailing technical improvements and innovative developments have been published.
A multitude of studies have simply failed to demonstrate improved outcomes.
A multitude of studies focusing on CFTR protein biochemistry have concluded that CFTR is a monomer [ 22- 26].
A multitude of studies have been conducted to investigate the efficacy of Aquamid to correct facial lipoatrophy in HIV patients.
