Finished lambleather from suppliers comes with different grades.The selection we ask is A-50%, B-30% and C-20%. Supplier's packing list showed A-70%, B-20% and C-10%. We did not find the 70%/20%/10% when we QC the shipment and usually the selection is lower. Obviously buyer and supplier's standard is different. I wonder if there is any problem with sampling method of the shipment.If our sampling size for inspection is 10% in quantity, should we draw from shipment using OUR's std A/B/C-50/30/20 (that is taking 50% in quantity from A grade and 30% in quantity from B grade ....) or Their's A/B/C-70/20/10. Will different sampling affect the final results?
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I must admit I know almost nothing about the leather industry. However, mathematically, I should think that the sampling results will be different, unless the stock is remarkably regular, though I doubt they will differ by much. As to which method you should use, I would say that depends on who the user of this information is. If, as I suspect, you must satisfy both your company and the supplier then I suggest this method: Instead of inspecting 10%, you must inspect 12%. This will of course require 20% more sampling than usual. Of this sample, 'A' will be 7/12, 'B' 1/4, and 'C' 1/6. Then, for your company's standard of 50/30/20, you multiply this measured 'A' by 5/7 and then use 'B' and 'C' as is. For the supplier's standard of 70/20/10, you use 'A' as is and multiply 'B' by 2/3 and 'C' by 1/2. I hope I have understood your problem correctly and you find this useful. I also hope you will post here how it all works out in the end.