Conceptual comparison of constructs as first step in data harmonization: Parental sensitivity, child temperament, and social support as illustrations

This article presents a strategy for the initial step of data harmonization in Individual Participant Data syntheses, i.e., making decisions as to which measures operationalize the constructs of interest - and which do not. This step is vital in the process of data harmonization, because a study can only be as good as its measures. If the construct validity of the measures is in question, study results are questionable as well. Our proposed strategy for data harmonization consists of three steps. First, a unitary construct is defined based on the existing literature, preferably on the theoretical framework surrounding the construct. Second, the various instruments used to measure the construct are evaluated as operationalizations of this construct, and retained or excluded based on this evaluation. Third, the scores of the included measures are recoded on the same metric. We illustrate the use of this method with three example constructs focal to the Collaboration on Attachment Transmission Synthesis (CATS) study: parental sensitivity, child temperament, and social support. This process description may aid researchers in their data pooling studies, filling a gap in the literature on the first step of data harmonization. • Data harmonization in studies using combined datasets is of vital importance for the validity of the study results. • We have developed and illustrated a strategy on how to define a unitary construct and evaluate whether instruments are operationalizations of this construct as the initial step in the harmonization process. • This strategy is a transferable and reproducible method to apply to the data harmonization process

Mechanical properties of polystyrene/low density polyethylene blends

Some mechanical properties of blends of polystyrene and low density polyethylene have been derived from stress-strain and impact measurements. The strength and impact properties are improved by adding a graft copolymer of polystyrene and low density polyethylene to the blends. It is assumed that the copolymer acts as an adhesive at the interface of the homopolymers thus decreasing the stress concentrations around the dispersed polymer particles at yield. The impact strength and modulus of polystyrene-graft copolymer blends could be made comparable to those of commercial rubber-modified impact polystyrenes by adjusting the fraction of copolymer in the blend

Particle dimensions in polystyrene/polyethylene blends as a function of their melt viscosity and of the concentration of added graft copolymer

Apparent particle dimensions in blends of low density polyethylene (PE) and polystyrene (PS) made by mixing in the molten state have been measured and have been shown to depend on the viscosity of the mixed system. At a certain shearing rate small particles of the dispersed polymer are obtained if the polymer in excess has a high viscosity. At a higher concentration however this effect is counteracted completely if the dispersed phase has a low viscosity and thus lowers the overall viscosity. Coalescence is affected in the same way and the size of the particles increases greatly with increasing concentrations. If a highly viscous polymer is dispersed in a low viscosity polymer matrix relatively large particle sizes will be found at the preset shearing rate mentioned above. With increasing concentration of the highly viscous dispersed phase the particle size decreases due to the increasing viscosity. This effect is counteracted by coalescence leading to a relatively slow increase of particle size with concentration. Addition of surfactants such as graft copolymers based on PS and PE leads to smaller particle sizes as expected