It is very useful to look at the big picture. We do this by looking at totals and summaries. For example, we may look at the total amount spent with a particular supplier and compare it with the amount spent with another supplier. Take a hypothetical case where the totals show that seven million dollars was purchased from supplier A last year whereas only five million dollars was purchased from supplier B. That indicates that supplier A received 40% more business than supplier B.

During the same period supplier A had five late deliveries and two rejections because of quality. Whereas supplier B had seventeen shipments arriving late and five shipments rejected because of poor quality.

These facts seem to clearly show that supplier A is a much better supplier than supplier B. A closer look at the data may cause some hesitation in making too quick a judgement. Purchases from supplier A are for only three items that have been thoroughly tested and produced for several years. Purchases from supplier B are for thirty-four complex items, many of which have just been introduced and for which the company has revised the specifications several times or more.

Supplier A may still possibly be the better source, but that conclusion cannot be reached by looking at the summary information only. The details tell much more and can often contradict what seems apparent.

Looking at the details only without looking at the aggregate may also produce information that leads to an incorrect conclusion. For example, it is common to over react to recent problems caused by a supplier. As a result users of the products involved may even ask purchasing to change suppliers. Before doing so, it is best to investigate the causes for the recent problems and look at the supplier’s total performance over time.