SPECULATIVE STORAGE, FUTURES MARKETS, AND THE STABILITY OF COMMODITY PRICES

A theoretical dynamic model is developed that integrates the micro-behavior of commodity and futures speculators into the simultaneous determination of cash and futures prices in a storable commodity market. The model is used to demonstrate the way in which the introduction of a futures market, by affecting the decisions of speculative inventory holders, alters the distribution of spot prices and to elucidate the conditions that render futures trading stabilizing for cash prices.     

The comparative analysis of the dynamics of childbearing women's birth at Yanging County, Beijing]

At the end of 1981 Yanging County had 26 communes, 375 production brigades and a total population of 211,098. A random sampling of 5.07% of the production brigades was taken, which included teams from the plains as well as mountainous regions. The sample had a population of 10,888, or 5.16% of the entire county, among whom 189 subjects were interviewed. These 189 women, whose ages ranged from 35-67, were divided into 5 birth year cohorts (1914, 1920, 1930, 1940, 1946). Findings include: 1) Age at marriage: the average age at marriage (about 17 years) between the 1914 and 1946 groups rose 1.82 years, indicating that early marriage was the norm. The time between marriage and 1st birth has shortened. 2) Fertility data: from 1914 to 1946 the lifetime fertility rate tended to decline from 4.60 to 3.70, but the 1930 cohort was the highest (6.42), followed by the 1920 cohort (6.26). The fertility rate of the 1914 cohort tended to rise in the 1950s after already having reached a peak in the early 1940s, probably because after Liberation fertility rose due to a higher standard of living and a stablized society. The fertility of the 1930 cohort was highest around 1963 when they were already 30 years old. The fertility of the 1940 cohort was also highest beginning around 1963. In both cases, the reason probably was because the national economy improved at this time. Indeed, the national fertility rate rose from a 1960 low of 20.9/1000 to 43.6/1000 in 1963. 3) Contraceptive use: prior to 1972 before there was an offical birth control policy, a sizeable number of women already desired to use contraceptives, the reason being most of these women felt they already had enough children. However, many women did use contraceptives in response to the call to do so. 4) Factors influencing fertility standards: in general, the less a woman's education and the lower her income, the higher was her standard of fertility, and vice versa. 5) The percentage of women who had children who died before the age of 15 ranged from 35.9% of the 67 year olds to 12.6% of the 35 year olds.     

Variations in carambola infestation rates byBactrocera carambolae drew and hancock (Diptera: Tephritidae) with fruit availability in a carambola orchard

The relationship between the infestation rate of carambola fruits byBactrocera carambolae Drew and Hancock was investigated in a carambola orchard. Phenology of the fruits was found to influence percentage infestation of fruits byB. carambolae. The proportion of unbagged or susceptible fruits infested varied with time of year and tended to decrease with the increase of unbagged fruits available on the tree. The number of ovipunctures per fruit varied with fruit size and was also found to be indicative of the number of adult insects (B. carambolae and parasitoids) that will emerge from each fruit. Higher number of susceptible fruits available on each tree also decreased both the number of ovipunctures per fruit and the number of eggs laid per fruit, which could possibly be due to the strategy of spreading the risk adopted by the femaleB. carambolae or a result of random selection with more hosts available. The main parasitoids recorded wereBiosteres vandenboschi (Fullaway) andB. arisanus (Sonan). The mean percentage of parasitism was 38.3% and it followed roughly that of infestation of fruits.     

M-Estimates of regression when the scale is unknown and the error distribution is possibly asymmetric: A minimax result

Huber (1964) found the minimax-variance M-estimate of location under the assumption that the scale parameter is known; Li and Zamar (1991) extended this result to the case when the scale is unknown. We consider the robust estimation of the regression coefficients (β₁,…,β_p) when the scale and the intercept parameters are unknown. The minimax-variance estimates of (β₁,…,β_p) with respect to the trace of their asymptotic covariance matrix are derived. The maximum is taken over ?-contamination neighbourhoods of a central regression model with Gaussian errors (asymmetric contamination is allowed), and the minimum is taken over a large class of generalized M-estimates of regression of the Mallow type. The optimal choice of estimates for the nuisance parameters (scale and intercept) is also considered.     

Developmental differences in baserate estimates of social behaviors and attitudes

This study examined the development of baserate estimation skills for everyday social events and attitudes. Subjects in grades one, three, and six responded to questions concerning their own rates of behavior and attitudes, and their estimates of baserates of behaviors and attitudes for their classmates. The findings indicate a general increase in accuracy for the estimation of baserates throughout the elementary school years. In addition, younger subjects were less likely to make similar estimates for themselves and their classmates than were older respondents. Developmental changes in estimation accuracy are discussed in relation to task content, use of the response scale, correspondence between self-reports and estimates, and sample variability.