Dawn,
I do not know if the following is an “effective” way of rating suppliers. It is taken from the Quality Engineering Handbook (Edited by Thomas Pyzdek and Roger W. Berger 1992, pp. 188-189) and paraphrased here.
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Supplier rating elements and formula are as diverse as companies are. The common aspects are quality and delivery. The quality factor usually includes quality lot rating and quality part rating. The delivery factor usually includes timeliness rating and completeness rating.
Quality Lot Rating is not equal to number of lots rejected divided by the number of lots inspected and Quality Part Rating is not equal to number of parts rejected divided by the number of parts inspected.
The timeliness rating is based on the due date of the lot minus some demerit (e.g. 10%) for each day the lot is early or late beyond some specified grace period or window.
The completeness rating equals the number of parts actually received divided by the number of parts scheduled to be received.
The overall rating can be derived by assigning percentages to the above.
Quality lot rating at 40% and quality part rating at 60% equals the quality rating.
Timeliness rating at 50% and completeness rating at 50% equals the delivery rating.
Quality lot rating at 70% and Delivery rating at 30% equals an overall supplier rating.
This generic example can be expanded into an elaborate computerized system and can be tailored for use by the small business.
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I do not particularly care for the above description. Years ago (too many, I’m afraid) I found a different system. I will try to find that and forward if available. Not sure if it will be any better, but it may be worth a try. Personally, I think rating suppliers is way overrated (so to speak).
Best Regards,
Don