T-SQL (SS2K8) :: How To Reduce Execution Time Of Median Calculations

I wrote a procedure to calculate median:

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ALTER proc [dbo].[sp_CalculateMedianTimeInDepartmentMinutes]

@StartDate date
,@EndDate date
as
--== Check if count is even or odd
declare @modulo int
select @modulo = (Select COUNT(*)%2 from ED_data where AdmitDateTime between @StartDate and @EndDate )
--=== Get Median

[Code] ....

My fellow developer is using this code to calcuate a madians in many columns (see below). The problem is that it takes about 2 minutes to execute this code. Is there a way to reduce the time of execution?

I attach also a sample of the view

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ALTER PROCEDURE [dbo].[sp_ED_Measures]
@StartDate date,
@EndDate date,
@Hospital varchar(5)
AS
BEGIN
SET NOCOUNT ON;

[Code] ......