Calculating Variation per Month

Hi,

I have a list of 35 000 sentences from which I extracted key words.

For each sentence, I have a rate and the date, from 2010 to 2019.

I would like to be able to see which are the keywords increasing/decreasing the most (variation of average rate per month) between minimum 5 differents years.

I'm a little lost to how to structure my DAX formula.

I was thinking to :

1) calculate average rate per month : I think I should use CALCULATE + AVERAGE + FILTER, but not sure how to calculate by month

2) I'm a little lost to calculate the variation

3) Display an histogram with the keyword with the TOP variation (increasing/decreasing)

I'm looking for some help to structure my think :)

Thanks