As far as I understand the following is in the present perfect continuous form, rather than in present perfect:
I’ve been thinking about majoring in business or economics.
In textbooks it is said that:
We use the Present Perfect Simple mainly to express that an action is completed or to emphasize the result. We use the Present Perfect Progressive to emphasize the duration or continuous course of an action.
So seems in the above case it is more appropriate to use present perfect tense. Isn't it? And if it is, than how we can do so.
Also is it correct to use present perfect continues without mentioning time period? And if it is, then how it is differ from Present Perfect.