DB Block Buffer Optimization in Version 6

One way to analyze that the data block buffers are utilized optimally, in version 7 is to measure the read hit ratio. The sql for that in version 7 would be:

select  1 - (sum(decode(name,'physical reads',value,0))/


	(sum(decode(name,'db block gets',value,0)) +


	(sum(decode(name,'consistent gets',value,0))))) "Read Hit Ratio"


from v$sysstat;
How does one go about getting this information in version 6?