Suggest an expression/filter please

[sravantig]

I have my DMR model, where I'm trying to create a chart.. below is a simple example in my list report

Year   Turnover rate   Centres               
1990   30%      Centres
1992   50%      Centres

My centres is a hierarchy with different layers like.. states, zone, district etc

Please suggest me a filter where I can display number of centres which are below 30% turnover rate.

[sravantig]

I tried filter
total([Turnover rate] for [Year],[Centres]) < 0.3
it gives me an error saying unsupported for clause.

Tried
filter([Centres], [Turnover Rate]<.3)
it gives me error
0061 filter evaluation must evaluate a boolean
the member caption can only be used inthe scope of cros tab or chart

Can anyone tell me what am I doing wrong?