Need a formula to identify trends and bias in data

Hi,

Apologies if this is a stupid question!

I need a formula to identify trends/bias in data. I analyse quality control data which compares the log difference between test and control samples. Then on a monthly basis the log difference is analysed for trends which for this purpose is considered to be where 5 consecutive values increase or decrease, or bias where 5 consecutive values return a positive or negative log difference.

Hope thats enough info, any help greatly appreciated!

I guess you should use charts for the same.