How many people have lived on the earth?

A simple formula is proposed for estimating the number of people who have ever lived. Using assumptions that seem reasonable, an estimate of 69 billion (1960) is obtained. The present world population is about 4 percent of this number.     

The Relations between Reactivity at 4 Months and Behavioral Inhibition in the Second Year: Replication across Three Independent Samples

This paper examines the predictive relations between two infant temperamental biases assessed at 4 months and inhibited behavior during the first 2 years of life in three independent samples from two research laboratories. Although each sample used slightly different criteria for classifying infants, the results across samples were consistent. Infants of both genders who displayed high levels of motor activity and distress to unfamiliar events were more inhibited at 14 months of age. By 24 months, there were significant sex differences: Boys identified as high reactive were more inhibited than high reactive girls.     

Personality predictors of career exploration: A meta-analysis

In this meta-analysis, correlations of personality traits and career decision-making self-efficacy with self and environmental career exploration were estimated across 71 samples and a pairwise sample of 19,846. Traits included the Big Five personality traits, shyness, locus of control, vocational decision styles, and stress. Many measures of career exploration were based on scores of self and environmental exploration on the Career Exploration Survey. Results varied by characteristics with the largest effects for locus of control, vocational decision style: thinking-feeling and self-efficacy. Environmental exploration and self-exploration were moderately correlated and demonstrated different relations with traits that were consistent with theory. Self-exploration was related to openness to experience and unrelated to extraversion, while environmental exploration was correlated with extraversion. Both were similarly correlated with conscientiousness such that conscientious individuals were more likely to engage in career exploration.