Screening Procedures to Identify Robust Product or Process Designs Using Fractional Factorial Experiments

In many quality improvement experiments, there are one or more ``control'' factors that can be modified to determine a final product design or manufacturing process, and one or more ``environmental'' (or `` noise'') factors that vary under field or manufacturing conditions. In many applications, the product design or process design is considered seriously flawed if its performance is poor for any level of the environmental factor. For example, if a particular prosthetic heart valve design has poor fluid flow characteristics for certain flow rates, then a manufacturer will not want to put this design into production. Thus this paper considers cases when it is appropriate to measure a product's quality to be its {\em worst} performance over the levels of the environmental factor. We consider the frequently occurring case of combined-array experiments and extend the subset selection methodology of Gupta (1956, 1965) to provide statistical screening procedures to identify product designs that maximize the worst case performance of the design over the environmental conditions for such experiments. A case study is provided to illustrate the proposed procedures

Selection and Screening Procedures to Determine Optimal Product Designs. (REVISED, April 1997)

To compare several promising product designs, manufacturers must measure their performance under multiple environmental conditions. In many applications, a product design is considered to be seriously flawed if its performance is poor under any level of the environmental factor. For example, if a particular automobile battery design does not function well under some temperature conditions, then a manufacturer may not want to put this design into production. Thus, in this paper we consider the overall measure of a given product's quality to be its worst performance over the environmental levels. We develop statistical procedures to identify (a near) the optimal product design among a given set of product designs, i.e., the manufacturing design associated with the greatest overall measure of performance. We accomplish this for intuitive procedures based on the split-plot experimental design (and the randomized complete block design as a special case); split-plot designs have the essential structure of a product array and the practical convenience of local randomization. Two classes of statistical procedures are provided. In the first, the delta-best formulation of selection problems, we determine the number of replications of the basic split-plot design that are needed to guarantee, with a given confidence level, the selection of a product design whose minimum performance is within a specified amount, delta, of the performance of the optimal product design. In particular, if the difference between the quality of the best and 2nd best manufacturing designs is delta or more, then the procedure guarantees that the best design will be selected with specified probability. For applications where a split-plot experiment involving several product designs has been completed without the planning required of the delta-best formulation, we provide procedures to construct a "confidence subset" of the manufacturing designs; the selected subset contains the optimal product design with a prespecified confidence level. The latter is called the subset selection formulation of selection problems. Examples are provided to illustrate the procedures

The Use of Subset Selection in Combined Array Experiments to Determine Optimal Product or Process Designs. (REVISED, June 1997)

A number of authors in the quality control literature have advocated the use of combined-arrays in screening experiments to identify robust product or process designs [Shoemaker, Tsui, and Wu (1991); Nair et al. (1992); Myers, Khuri, and Vining (1992), for example]. This paper considers a product manufacturing or process design setting in which there are several factors under the control of the manufacturer, called control settings, and other environmental (noise) factors that that vary under field or manufacturing conditions. We show how Gupta's subset selection philosophy can be used in such a quality improvement setting to identify combinations of the levels of the control factors that correspond either to products that are robust to environmental variations during their use or to processes that fabricate items whose quality is independent of the variations in the raw materials used in their manufacture. [Gupta (1956, 1965)]

Emergency department visits for traumatic brain injury in a birth cohort of medicaid-insured children

Objectives: To analyse emergency department-based data on paediatric traumatic brain injury (TBI). Methods: This study constructed a retrospective cohort of 493 890 children who were born in New York City between 1999–2007 and who were enrolled in the New York Medicaid programme at the time of their birth and followed these children from birth to the end of 2007. Results: There were 62 089 injury-related emergency department visits, of which 1290 had ICD-9 codes consistent with TBI. Children with TBI were more likely to be male (59.4% vs 51.4%) and Hispanic (43.9% vs 26.3%) than those in the underlying birth cohort and were more than twice as likely to be admitted to the hospital for inpatient care (RR = 2.4, 95% CI = 2.2, 2.6). The most commonly listed cause of injury was falls (58.3%). Spatially-smoothed risk estimates indicated that some areas of the city are associated with a greater risk of paediatric TBI than others. Conclusions: Emergency department data can be used to describe paediatric TBI in ways not easily available through more routinely collected administrative health data. This information can be used to target prevention and control efforts

Genome-wide linkage analysis of the tracking of systolic blood pressure using a mixed model

BACKGROUND: Elevated blood pressure in middle age is a major risk factor for subsequent cardiovascular complications. An important longitudinal characteristic of blood pressure is the "tracking phenomenon". Tracking is defined as the persistence of the rank of a person's blood pressure level in a group over a long period of time. In this analysis, we used the Framingham data to investigate whether there are some genes responsible for this phenomenon. RESULTS: Both two-point and multipoint linkage analyses were applied to family members with complete data only and to all family data with missing values imputed by a Gaussian model. The results of two-point linkage analysis indicated that two loci for linkage with the intercept were on chromosomes 10 and 13, and two loci for linkage with both slope and intercept were on chromosomes 1 and 3. Multipoint linkage analysis indicated only one region, 200–240 cM on chromosome 1, to be linked with both intercept and slope. For the intercept of SBP, the highest LOD (4.43) was found at 214 cM when missing data were imputed, and the highest LOD (2.81) was at 231 cM for the complete case data. For the slope of SBP, the highest multipoint LODs were 3.63 at 227 cM and 2.02 at 234 cM for the complete case data and imputation data, respectively. CONCLUSION: One or more genes in the range of 200–240 cM on chromosome 1 may be related to the tracking phenomenon of SBP

National Safe Routes to School program and risk of school-age pedestrian and bicyclist injury

Purpose Safe Routes to School (SRTS) was a federally funded transportation program for facilitating physically active commuting to and from school in children through improvements of the built environment. There is evidence that SRTS programs increase walking and bicycling in school-age children, but their impact on pedestrian and bicyclist safety has not been adequately examined. We investigate the impact and effects of the SRTS program on school-age pedestrian and bicyclist injuries in a nationwide sample in the United States. Methods Data were crash records for school-age children (5–19 years) and adults (30–64 years), in 18 U.S. states for a 16-year period (1995–2010). Multilevel negative binomial models were used to examine the association between SRTS intervention and the risk of pedestrian and bicyclist injury in children aged 5–19 years. Results SRTS was associated with an approximately 23% reduction (incidence rate ratio = 0.77, 95% confidence interval = 0.65–0.92) in pedestrian/bicyclist injury risk and a 20% reduction in pedestrian/bicyclist fatality risk (incidence rate ratio = 0.80, 95% confidence interval = 0.68–0.94) in school-age children compared to adults aged 30–64 years. Conclusions Implementation of the SRTS program appears to have contributed to improving traffic safety for school-age children in the United States

Surfactant-aided exfoliation of molydenum disulphide for ultrafast pulse generation through edge-state saturable absorption

We use liquid phase exfoliation to produce dispersions of molybdenum disulphide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical structures of the bile salt surfactants play a crucial role in the exfoliation and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched in single and few (<6) layer flakes with large edge to surface area ratio. We use the dispersions to fabricate free-standing polymer composite wide-band saturable absorbers to develop mode-locked and Q- switched fibre lasers, tunable from 1535-1565 and 1030-1070 nm, respectively. We attribute this sub-bandgap optical absorption and its nonlinear saturation behaviour to edge-mediated states introduced within the material band-gap of the exfoliated MoS2 nanoflakes.Comment: 6 pages, 5 figure