Sampling with probabilities proportional to the variable of interest

To estimate the mean sojourn time, a sample of Tilburg fair visitors was asked for the duration of their stay on the fair grounds. The longer a visitor's sojourn, the larger his/her probability of being interviewed will be; therefore, longer sojourn times will be overrepresented in the sample. As a consequence, the arithmetic sample mean is not a suitable estimator. The paper places this problem against a theoretical background. As a better estimator the harmonic mean of the observed sojourn times is presented. In addition, a variance estimator is given. The properties of these estimators are difficult to derive analytically. Instead, their behaviour is studied in a number of examples.Probability;Estimation;Sampling;statistics

SHELF LIFE OF DODOL PACKED BY EDIBLE FILM

The aim of the study was to determine the shelf life of dodol packed by edible film. Dodol, food product made from a mixture of sugar and lipid, was studied by using packaging and without packaging. The edible film was used as packaging. The results showed that dodol packed by edible film had a significant effects on its water contents and total yeast and molds. These may extend the shelf life until 9 days

Fixed export costs and multi-product firms

This paper has two aims. First, we uncover some salient components of fixed export costs, which play a crucial role in recent heterogeneous firms models of international trade. Second, we investigate whether the importance of these fixed export costs varies with the size of a firms export product portfolio. We find that a destination country's institutional quality, such as the quality of regulation or the extent of corruption, form important impediments to a firm's export decision, lowering the export probability by up to 10%-points. Moreover, relative to single-product firms, multi-product firms experience additional export probability decreases of around 2%-points

Knowledge diffusion from FDI and intellectual property rights

We study the extent to which a country's strength of Intellectual Property Rights (IPR) protection mediates knowledge spillovers from Foreign Direct Investment (FDI). Following the opposing views in the IPR debate, we propose a negative effect of IPR strength on unintentional horizontal (intra-industry) knowledge diffusion. Using a unique firm-level dataset of large, publicly traded firms in 22 (mostly) developed countries, we find partial support for these expectations. Strong IPR indeed reduces horizontal knowledge diffusion, while it stimulates backward (to suppliers) knowledge diffusion. Somewhat unexpectedly however, we also find that forward (to customers) knowledge diffusion decreases with IPR strength. In general, and in line with earlier literature, the results regarding backward knowledge diffusion are most robust to changes in model specification. Our results contribute to the debate regarding the desirability of strengthening national IPR systems, and suggest that local firms might indeed benefit from this through their (backward) linkages with multinationals. Additionally, our results suggest that the moderating effect of IPR strength might partly explain the inconclusive results in the FDI knowledge diffusion literature

Judging an unfamiliar object’s distance from its retinal image size

How do we know how far an object is? If an object's size is known, its retinal image size can be used to judge its distance. To some extent, the retinal image size of an unfamiliar object can also be used to judge its distance, because some object sizes are more likely than others. To examine whether assumptions about object size are used to judge distance, we had subjects indicate the distance of virtual cubes in complete darkness. In separate sessions, the simulated cube size either varied slightly or considerably across presentations. Most subjects indicated a further distance when the simulated cube was smaller, showing that they used retinal image size to judge distance. The cube size that was considered to be most likely depended on the simulated cubes on previous trials. Moreover, subjects relied twice as strongly on retinal image size when the range of simulated cube sizes was small. We conclude that the variability in the perceived cube sizes on previous trials influences the range of sizes that are considered to be likely. © ARVO

The effect of variability in other objects’ sizes on the extent to which people rely on retinal image size as a cue for judging distance

Retinal image size can be used to judge objects’ distances because for any object one can assume that some sizes are more likely than others. It has been shown that an increased variability in the size of otherwise identical target objects over trials reduces the weight given to retinal image size as a distance cue. Here, we examined whether an increased variability in the size of objects of a different color, orientation, or shape reduces the weight given to retinal image size when judging distance. Subjects had to indicate the 3D position of a simulated target object. Retinal image size was given significantly less weight as a cue for judging the target cube’s distance when differently colored and differently oriented target objects appeared in many simulated sizes but not when differently shaped objects had many simulated sizes. We also examined whether increasing the variability in the size of cubes in the surroundings reduces the weight given to retinal image size when judging distance. It does not. We conclude that variability in surrounding or dissimilar objects’ sizes has a negligible influence on the extent to which people rely on retinal image size as a cue for judging distance

Does size matter?

For isolated objects in complete darkness, retinal image size contributes to distance judgments even if the true object size is unknown. Here we show that the same is true under more natural conditions. On a wide beach we positioned a red cube at 10–20 m distance and then asked subjects to walk to it while blindfolded. Subjects never had a close view of the cube and were unaware that on separate trials cubes with sides of 15 cm and 20 cm were positioned at the same locations. On average, subjects walked 1 m further after seeing the 15 cm cube than after seeing the 20 cm cube

The influence of previously seen objects' sizes in distance judgments

An object's retinal image size is determined by a combination of its physical size and its distance, so judgments of an object's size and distance from its retinal image size are coupled. Since one does not have direct access to information about the object's physical size, people may make assumptions about how large it is likely to be. Here we investigated whether the sizes of similar, previously encountered objects influence the assumptions about the physical size of an object and therefore the interpretation of its retinal image size in terms of its distance. Subjects moved their unseen index finger to the positions of binocular simulations of red cubes. For identical target cubes at the same position, they indicated a nearer position of the cube when the preceding cube was small than when it was big. This is in agreement with a tendency to expect the cube to be the same size as that on the previous trial. However, if the expectation were simply adjusted slightly on each trial, the cube would be judged to be nearer when preceded by two consecutive smaller cubes than when preceded by only one smaller cube. It was not, so there must be a more direct influence of the size in the previous trial on distance judgments