Difference between two percentages using a filtered percentage and 'all sample' percentage

[MichaelBauld]

Hi everyone,

I have a survey which I am producing a report for and I would like to show the % difference between a filtered total of responses and a 'total sample' measure. For example:

Age Range	Responses filtered by various slicers (e.g. sampling location)	Total sample (only affected by calendar slicer)	% difference
16-24	20%	30%	-10%
25-34	40%	40%	0%
35-44	40%	30%	+10%

To get the % total for each category which responds to the various slicers I have used the following formula, but this is only half of the equation:

% Age Range = DIVIDE(COUNT(Data[Which age group are you in?]),CALCULATE(COUNT(Data[Which age group are you in?]),ALL(Data[Which age group are you in?])))

To make matters more complicated, for some of the tables I am using a dimensions table to convert the variable key into a more relevant description. i.e. the raw data holds age range codes from 1-8 which equate to typical age range brackets listed in the dimensions table (16-24, 25-34 etc). Unfortnately the formula above doesn't work in this context.

Question: 

1: Does anyone know how I could re-write this to prevent any filters from affecting it (except date range) to create a 'whole sample' measure?

2: Is there a way of writing this to allow it to work using the dimension table 

I've mocked up a simple version of the data model here so you can see what I am trying to accomplish.

Thank you in advance for any help with this!

Kind regards

Michael