I recently wrote one letter about the Passive smoking effects to practice my self in writing , in one paragraph i wrote: "the passive smoking phenomenon according to many researches can cause a variety of diseases like...."

Some one told me that the expression «according to many researches" is wrong, could some one help me to correct it please?

Thanks in advance.

according to many researchers

according to a lot of research

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we say "much research" rather than "many researches".
Strange, but Cambridge dictionary says it's ok to use researches...
research noun [ U ] uk /rɪˈsɜːtʃ/ /ˈriː.sɜːtʃ/ us /ˈriː.sɝːtʃ/ /rɪˈsɝːtʃ/ UK also researches [ plural ]
UK His researches in the field of disease prevention produced unexpected results .
which one is correct?

This methods..... or this method........

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Since then, much research has been done in this area, and scientists have found that graphene has unique and strange properties