After the trial orders are executed, it becomes necessary for the buyer to rate the vendors to enable him to determine how he should apportion his requirements among the vendors.
In other words, the basic responsibility of the materials manager is not only to locate the sources but also to preserve them through continuous rating. A vendor’s performance in meeting the quality, delivery and price standards set by the buyer has to be assessed in a systematic manner.
Techniques of Vendor Rating:
The purchase organizations watch his enlisted suppliers continuously and take requisite corrective action. Following rating plans are utilized for vendor rating:
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(a) Categorical plan
(b) Weighted point plan
(c) Cost ratio method
(d) Eavaston’s vendor selection
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(e) Forced decision matrix
(f) Service cost ratio
(g) Bell quality rating system
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(h) IBM quality rating system.
(a) Categorical Plan:
The categorical plan is a sample of all vendor rating schemes. It relies heavily on the judgement and experience of the decision maker. The purchaser maintains a list of his suppliers and their products. The vendor performance is reviewed periodically by an evaluation committee comprising of all representatives.
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Depending upon the performance, the vendor is given a plus point, neutral or minus. The performance trends over a period of time are built up and the vendor with increasing trend of plus point is chosen. A preponderance of pluses or minuses needs notification to supplier with comments.
On the basis of experience and periodical meetings, a list of factors can be established on the suppliers’ performance in each area and each factor is given a grading as ‘never’, ‘seldom’, ‘usual’, ‘always’, etc. This system, though non-quantitative, provides a means of systematic record keeping on performance criteria.
(b) Weighted Point Plan:
Quality, delivery or service and price are the three most important attributes of a good supplier. Depending upon the importance, a purchaser attaches to a particular attribute he fixes a weightage for it. The total weightages are being 100. The weightages, for example, of the attributes are as follows:
Quality — 60%
Delivery — 25%
Price — 15%
The quality rating (Table 15.1), delivery (service) rating (Table 15.2), price rating (Table 15.3) and composite rating (Table 15.4) are calculated.
The weighted point plan technique enables a purchaser to evaluate a supplier on quantitative basis. This plan is more objective than categorical plan and the only way the subjectivity can enter is while assigning the weights. Proper records have to be kept.
If services of a computer are available, then this plan can be used very successfully. Under this plan, the supplier can be classified as excellent, acceptable, average and unacceptable if their composite rating is over 90%, between 75% and 90%, between 60% to 75% and below 60%.
(c) Cost Ratio Method:
This method relates to identifiable purchasing and receiving costs to the value of shipment received from respective suppliers. The higher the ratio of costs to shipments, the lower the rating applied to the supplier: Quality, delivery, service and price are the usual categories to which costs are allocated, after subdividing each factor into various elements.
The respective cost ratios are suitably combined with the vendors’ quoted price, to determine the net cost. Here, the vendor performance is reviewed periodically by an evaluation committee comprising of representatives from all departments involved with purchasing.
(d) Eavaston’s Vendor Selection:
The suppliers’ past performance is utilized in the choice of vendors and the basic steps in this method are as follows: (i) The vendors on the approved list are ranked on the basis of the buyer’s subjective evaluation, (ii) The first satisfactory vendor, meeting or exceeding all the standards, (iii) If the applied vendors do not fulfill the minimum standards, then the minimum standard may be relaxed till a vendor is chosen. It presupposes that standards of acceptability for every criterion are formed to fit in order to take decisions.
(e) Forced Decision Matrix:
The attributes of rating like price, quality, service, reliability of the supplier, lead time of supply etc. — are identified first. Then these factors are compared between themselves, like quality and price. If price is considered more important than quality by the evaluation committee, then a weightage of one is given to price and zero to quality.
The quality is compared with each of the remaining factors and the relative weightages are recorded in the form of a table or matrix. Similarly, each factor is compared in turn with each of the others and their relative weightages are recorded. Weightages given to the different attributes are added up for each attribute and divided by the total number of comparisons to give the attribute weightage co-efficient for each attribute.
After this, the next step is to compare the suppliers in pairs in respect of each attribute, giving the superior supplier a weightage of one and the other. These results are tabulated and the supplier weightage co-efficient is thus obtained.
The above two types of coefficients are combined by multiplying for each attribute and for each supplier. These are then added up to give the total weightage and this is ranked to take the appropriate decisions on the vendors. The weightage can be varied and the matrix can be suitably built for a large number of suppliers and evaluators.
(f) Service Cost Ratio:
There are other intangible aspects of a supplier’s services. They can only be measured subjectively. The procedure is as follows:
(i) Listing the service factors like R&D, Labour stability, financial stability, flexibility in production for rush orders, etc.
(ii) Assigning weights to each factor according to its importance to the purchaser.
(iii) Setting an acceptable norm e.g., out of a total of a 100 service points 70 may be an acceptable norm.
(iv) Rating suppliers for each service factor.
(v) Determining the percentage by which the supplier is over or under the acceptable norm.
(vi) Multiplying the percentage obtained in (v) by value of package percent. For sophisticated items the value of package percent may be 10% and for common Bazzar items it may be just 1%.
(vii) The percentage figure arrived at in (vi) is minus if the percentage in (v) is over the acceptable norm and is plus if it is below the acceptable norm.
The sample procedure of calculating the service cost ratio is shown in table 15.5.
(g) Bell Quality Rating System:
The bell helicopter company developed a Lot Quality Index (LQI), which give an assessment of all lots received against lots rejected, by disposition and category, as the company attaches greater importance to quality. The LQI is given by: LQ1 – X/L, where
L = total number of lots received during the period, x = (L1 x 1.00) + (L2 x 2.10) + (L3 x 2.90) + (L4 x 3.10)
+ (L5 x 3.90)
L1 = Number of lots acceptable as received
L2 = Number of lots rejected by sampling inspection but labelled.
L3 = Number of lots rejected and dispositioned, rework at supplier’s end.
L4 = Number of lots rejected and dispositioned, returned not usable and
L5 = Number of lots rejected and dispositioned rework at Bell helicopter company.
The weights 1.00, 2.10 etc. were determined at the company after a careful study of the complexity and number of operations required to have a usable lot from a particular dispositioned lot. It is clear from the above equation, that the best lot quality index figure rates is 1.0, the worst is 3.90. The formula can be modified easily to suit the needs of a particular firm. The quality rating can be combined with rating for other parameters, to develop suitable vendor rating schemes.
(h) IBM Quality Rating System:
The IBM rating system uses quality costs as the basis for rating suppliers. The formula for the vendor quality rating is:
VGR = Desired cost of inspection / Actual cost of inspection x 100
The cost incurred in inspecting acceptable material is the desired cost, the cost of inspecting rejected material being excluded from it. The actual cost of inspection includes cost incurred in inspecting acceptable as well as rejected material plus cost associated with extra handling of rejected material.
Inspection cost is obtained by multiplying the actual time spent on inspection by the standard rate. The material handling cost is found by multiplying the number of documents to process the rejected material by a standard cost.
Advantages:
The IBM quality rating system the following advantages:
(a) Factors of cost used are well understood by the suppliers,
(b) All rating factors are brought down to common basic costs and can therefore be combined even if the factors themselves are different.
(c) Some minor defects are allowed, so long as the quality requirements are clearly met.
(d) It establishes a long range goal of what a good supplier should supply.
(e) No complicated weighting factors are required.
(f) When cent percent inspection is required, it provides for equitable rating.
(g) When cent percent inspection is required, it considers the inspection cost.
(h) The same data can be used to find out which suppliers, cost the company more and which items require more inspection time. Based on the information, inspection methods may be improved and attention can be directed towards the costly suppliers.
The IBM system on quality rating is useful, when there are a large number of suppliers vending several products. The inspection information is fed directly into the computer (or accounting machine), which computes the ratings and summarizes the information in various ways, like type of defects, part number, supplier code, final product etc. for further analysis.