Testing change between 2 samples at 2 periods of time

#1
Hi

Id wonder if anyone could help me. Im having one of those brain freeze moments when you think you may know the answer but really would appreciate a second opinion…

Im looking at change between two points of time (from two cross sectional surveys conducted in 2006 and 2008) for 2 areas (say area X and area Y). Am I right in thinking area X change would be significant compared to area Y change if the minimum change for area X from CI’s is greater than the max change by area Y from CI’s. Im using confidence intervals for proportions

e.g. For a hypothetical question
Area X Area Y
2006 2008 2006 2008
Percentage stating 'Z' 50.0 51.4 60.0 60.2
Upper CI 50.8 52.2 61.8 61.9
Lower CI 49.2 50.6 58.2 58.5





So from the table above:

Area X min change = 50.6 - 50.8 = -0.2 i.e lower ci 2008 – upper ci 2002
Area Y max change = 61.9 - 58.2 = 3.7 i.e upper ci 2008 – lower ci 2002

Min change for area X is not greater than max change for area Y = difference in change is not significant

Or am I completely of the mark with how I am trying to do this. In the back of my head I think I may be terming some differences not significant when in fact they are significant.

Thanks for any help they you can provide

Ian

My head is hurting from going round in circles!