Sequential Sampling within a Portable Computing Environment
BACKGROUND: In industrial, agricultural, and warehouse/retail settings, there are many situations where sequential sampling and hypothesis testing could markedly improve productivity and quality control. However, the underlying mathematics can be very complicated, leading to very high computing requirements. Also, the logistics of sequential data collection is difficult. Thus, existing systems typically use simplified protocols (e.g. fixed sample sizes) or use advanced hardware that is relatively expensive and immobile. Thus, there is a need for more compact, portable systems that can implement dynamic decision-making protocols with flexible sampling and statistical testing.
DESCRIPTION: University of California (UC) researchers have developed a sequential sampling tool that can execute advanced dynamic protocols on a convenient portable platform. The UC researchers built a prototype of this system consisting of a laptop computer and software code compiled with well-known statistical and graphical user interface packages. This prototype is undergoing tests in a pest monitoring application, where sequential sampling and analysis of the density of citrus pests like citricola scale and California red scale could enable one to accurately assess the threat posed by these pests and thus spray pesticides in a more economical manner. Their prototype processes input data in real time and display instructions to the user as to whether or not to take additional samples, significantly reducing the burden of data collection as compared to fixed-size sampling methods. This has the potential to reduce the costs of active pest monitoring to the point where it becomes a cost-effective means for optimizing the application of pesticides.
The UC sampling & testing tool supports SPRT, 2-SPRT, and sequential sampling protocols for a variety of statistical distributions, including Bernoulli, binomial, Poisson, negative binomial, and normal distributions. The user has easy access to properties of the statistical design such as average sample size and the type-1 and type-2 errors for the design. It also displays boundary lines for the design and allows the user to plot and visualize each sample point one-at-a-time as each sample unit is taken and counted. When points cross over one of the two boundaries, the tool alerts the user as to which of the two hypotheses is more likely (figure 1). The software can also export data to common file formats used for reports. The researchers anticipate that this range of functionality could be realized in an even more compact device—one could manufacture a handheld version of the tool with an embedded operating system that would be capable of running their software.
APPLICATIONS: In addition to the pest assessment & control application supported by the original prototype, this invention may find use in quality control and product acceptance testing applications, particularly in applications where the hardware needs to be portable and the hypothesis testing must be carried out in real time.
ADVANTAGES: The UC sampling & testing tool is the first of its kind, making it possible to use complex sequential sampling methods in a relatively inexpensive portable computer. This invention potentially only requires a proprietary software module to be combined with off-the-shelf hardware and supporting software components, facilitating the development of different versions of the tool for different applications and for a variety of hardware platforms and operating systems.
PATENT STATUS: US Publication No. 20080114567 published May 15, 2008
FIGURE 1—Screenshot of the prototype software showing sequential data from 36 samples with dynamic sampling boundaries under 2-SPRT for testing H0:μ=7 versus H1:μ=10. The upper boundary is crossed by the 35th sample.
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