A lot sampling plan is a sampling scheme and a set of rules for making decisions. The decision, based on counting the number of defectives in a sample, can be to accept the lot, reject the lot, or even, for multiple or sequential sampling schemes, to take another sample and then repeat the decision process. The sampling plans fall into the following categories:
1. Single sampling plans:
One sample of items is selected at random from a lot and the disposition of the lot is determined from the resulting information.
These plans are usually denoted as plans for a sample size n, where the lot is rejected if there are more than c defectives. These are the most common (and easiest) plans to use although not the most efficient in terms of average number of samples needed.
2. Double sampling plans:
After the first sample is tested, there are three possibilities:
1. Lot acceptance.
2. Lot rejection.
3. No decision.
If the outcome is (3), and a second sample is taken, the procedure is to combine the results of both samples and make a final decision based on that information.
3. Multiple sampling plans:
This is an extension of the double sampling plans where more than two samples are needed to reach a conclusion. The advantage of multiple sampling is smaller sample sizes.
4. Sequential sampling plans:
This is the ultimate extension of multiple sampling where items are selected from a lot, one at a dame and after inspection of each item a decision is made to accept or reject the lot or select another unit.
5. Skip lot sampling plans:
Skip lot sampling means that only a fraction of the submitted lots are inspected.
The Value Method was originally developed by Larry Mills of General Electric (GE) in 1943. It has been highly refined and honed by many over the years.
It employs highly efficient procedures that are consistent with sound management techniques and is tuned to achieve maximum performance in the minimum amount of time required.
As a complete and mature process with more than 50 years of successful application, it has been used in almost any endeavor contemplated.
The Value Method is a highly efficient and productive decision-making process and employs:
a. Systematic and organised procedural processes.
b. Creative methods to generate alternatives.
c. Essential functional approach.
d. Comparisons of worth as opposed to Life-Cycle Costs (defined as value).
Several characteristics differentiate the Value Method from other techniques. These help ensure that the customer obtains the kind of product they need and want.
a. Value-based decision process
b. Uses functional approach
c. Follows a very systematic and organized “job plan”
d. Directs efforts towards maximum possible alternatives through creativity techniques.
In Value Analysis multifunctional teams (design, production engineering, purchasing, and quality) use a formalized process to identify alternative materials, manufacturing processes, and designs to improve function while reducing costs.