is missing function

[cognos05]

Hi,
I have two types of users one admin and other test user. I will show level 5 and  level 4 as nested rows in my report. Admin will have access to these levels, but test users will have access to only few products fn level 5 and level 4.

So explicitly to show only level 3 items for test users for which they have access , I use a data item with below expression .
filter(members([Sales].[Item Numbers].[Item Numbers].[Level 3]), parent(currentMember([Distributor Sales].[Item Numbers].[Item Numbers]) is missing)

so this gives me the level 3 items for the test users if they dont have access to level 5 and level4 but have access to level 3.

This works fine when logged as test users, but when logged as admin , it gives me level 5 and level 4 for the products ,but sometimes gives the level 3 also.

Is there any alternate function for " is missing" or any other way to go about it.

This is a dimensional package.

Thanks,
Nithya