I looked "kind" up in dictionary: nature or character as determining likeness or difference between things, the nature, or natural disposition or character. The two interpretation are kind of similar. In your expression, the former means two thing, the later means one thing, So,it seems that you can have it the both way, but I don't know if the former is a common expression.

"the kinds of research methods" = if you are talking about more than one method "The kind of research method" = if you are talking about only one method

The correct is : the kinds of research method