% Change Last Year

[amandabus21]

How can I find out how to create a percent change from last year?

The caculation displayed in the table is: 

Accidents Per 100K Miles = DIVIDE('Datamart AccidentSummary'[Sum of PV],'Datamart AccidentSummary'[Sum of Mileage]) *100000

I need the percent change of "Accidents last year per 100k miles", on a monthly basis and YTD total. 

[Greg_Deckler]

@amandabus21 Here are a couple of approaches:

Better Year Over Year Change = 
    VAR __Year = MAX('Table'[Year])
    VAR __Curr = SUMX(FILTER(ALL('Table'),[Year] = __Year),[Value])
    VAR __Prev = SUMX(FILTER(ALL('Table'),[Year] = __Year - 1),[Value])
RETURN
    DIVIDE(__Curr - __Prev, __Prev, 0)



Better Year Over Year Change 2 = 
    VAR __Year = MAX('Table'[Year])
    VAR __EndDate = MAX('Table'[Date])
    VAR __StartDate = MIN('Table'[Date])
    VAR __PrevDateEnd = DATE(YEAR(__EndDate) - 1, MONTH(__EndDate), DAY(__EndDate))
    VAR __PrevDateStart = DATE(YEAR(__StartDate) - 1, MONTH(__StartDate), DAY(__StartDate))
    VAR __Curr = SUMX(FILTER(ALL('Table'),[Year] = __Year),[Value])
    VAR __Prev = SUMX(FILTER(ALL('Table'),[Date] <= __PrevDateEnd && [Date] >= __PrevDateStart),[Value])
RETURN
    DIVIDE(__Curr - __Prev, __Prev, 0)

Since you have a single table data model, the default Power BI quick measure won't work correctly.

[amandabus21]

@Greg_Deckler Thank you for your help!

So I created the measure:

Better Year Over Year Change =

    VAR __Year = MAX('Datamart AccidentSummary'[Fiscal_Year])

    VAR __Curr = SUMX(FILTER(ALL('Datamart AccidentSummary'),[Fiscal_Year] = __Year),[Accidents Per 100K Miles])

    VAR __Prev = SUMX(FILTER(ALL('Datamart AccidentSummary'),[Fiscal_Year] = __Year - 1),[Accidents Per 100K Miles])

RETURN

    DIVIDE(__Curr - __Prev, __Prev, 0) 

 That is giving me this:

which is not quite the numbers im looking for.

 Here is a better picture of what Im looking to recreate in Power BI 

If you see for 2016/2017 in January, the % change is -2.3%