selected value -1 - custom periods headcount

[olciasandra]

Hi, 

Could you please help me with the below? 

I have a list of employees IDs for the last two years.  Next to that I have a custom period that we are using instead of months. I've added an index column matching the custom periods from the beginning until the end of our "custom calendar". 

I am trying to find a way that the customer will filter the report eg. 2018p9 and he or she will get the headcount difference 2018p9-2018p8.

I've added three measures:

Current Period = calculate(DISTINCTCOUNT('DATA BASE'[Employee ID]),FILTER(('DATA BASE'),'DATA BASE'[Index - YP]=SELECTEDVALUE('DATA BASE'[Index - YP])))

Prev.YP = CALCULATE(SELECTEDVALUE('DATA BASE'[Index - YP])-1)   

Previous period = calculate(DISTINCTCOUNT('DATA BASE'[Employee ID]),FILTER('DATA BASE',[Prev.YP]))

 It seems that previous period headcount is not counting properly, so the differenct between two periods is not correct. 

Could you please help?

Below the table with example. 

Employee ID	Custom period	Index-YP [index column]
123	2018p1	1
123	2018p2	2
456	2018p3	3
789	2018p4	4
234	2018p5	5
123	2018p6	6
...	2018p7	7
..	2018p8	8
...	2018p9	9
..	2018p10	10
..	2018p11	11
..	2018p12	12
..	2018p13	13
	2019p1	14
	2019p2	15
	2019p3	16
	2019p4	17
	2019p5	18