Examines the undercount problem in the 1990 census, the ways in which the Census Bureau has dealt with it in the past, and the Bureau's plans to avoid future undercounts. It also discusses the statistical concept of dual systems estimation in census counting as a means of lessening an undercount. (GR)

Studied accuracy and use of sequence number string in hearing 3- to 5-year-olds and in deaf 4- to 6-year-olds using the Belgian French Sign Language. Found that deaf children exhibited age-related lags in knowledge of the number sequence, and made different errors from those of hearing children, reflecting the rule-bound nature of sign language.…

Two experiments explored effects of intervention and test conditions on preschoolers' use of counting to compare two sets. At mean age of 4 years 4 months, children in two intervention groups were more likely to use counting to compare sets than those in control group. Use of counting to compare sets was closely related to counting performance.…

Preschoolers' performance on a matching task and a counting task suggested that most four-year-old children and some 3 1/2-year-old children used number words to denote one-to-one correspondence in the tasks. (RH)

A recursive equation is proposed for computing higher order derivatives of elementary symmetric functions in the Rasch model. A simulation study indicates a small loss in accuracy for the proposed formula compared to Gustafsson's sum algorithm (1980) for computing higher order derivatives when tests contain 60 items or less. (SLD)

Two studies examined age-related declines in the functioning of working memory. Negative correlations between age and measures of working memory were found. These relations were attenuated by measures of storage capacity, processing efficiency, coordination effectiveness, and simple comparison speed. The greatest attenuation occurred with simple…

Presents two alternative computational procedures for solving the modified Bessel equation of zero order: the Frobenius method, and the power series method coupled with a curve fit. Students in heat transfer courses can benefit from these alternative procedures; a course on ordinary differential equations is the only mathematical background that…

The coding of time in growth curve models has important implications for the interpretation of the resulting model that are sometimes not transparent. The authors develop a general framework that includes predictors of growth curve components to illustrate how parameter estimates and their standard errors are exactly determined as a function of…

Conventional wisdom in missing data research dictates adding variables to the missing data model when those variables are predictive of (a) missingness and (b) the variables containing missingness. However, it has recently been shown that adding variables that are correlated with variables containing missingness, whether or not they are related to…

The heliocentric, or Sun-centered model, one of the most important revolutions in scientific thinking, allowed Nicholas Copernicus to calculate the periods, relative distances, and approximate orbital shapes of all the known planets, thereby paving the way for Kepler's laws and Newton's formation of gravitation. Recreating Copernicus's…

Five-year-old children categorized as skilled versus unskilled counters were given verbal estimation and number word comprehension tasks with numerosities 20-120. Skilled counters showed a linear relation between number words and nonsymbolic numerosities. Unskilled counters showed the same linear relation for smaller numbers to which they could…

According to one theory about how children learn the concept of natural numbers, they first determine that "one", "two", and "three" denote the size of sets containing the relevant number of items. They then make the following inductive inference (the Bootstrap): The next number word in the counting series denotes the size of the sets you get by…

Current descriptions of results from hierarchical linear models (HLM) and hierarchical generalized linear models (HGLM), usually based only on interpretations of individual model parameters, are incomplete in the presence of statistically significant and practically important "slopes as outcomes" terms in the models. For complete description of…

Multilevel analysis is an appropriate tool for the analysis of hierarchically structured data. There may, however, be reasons to ignore one of the levels of nesting in the data analysis. In this article a three level model with one predictor variable is used as a reference model and the top or intermediate level is ignored in the data analysis.…