In short, the effect reported by AH is sensitive to alternative model specifications, and one should be cautious when drawing conclusions about the impact of being a nine-ender on suicidal behavior on the basis of the evidence presented by AH. AH provide no motivation for the inclusion of the covariates or examine how the results are conditional upon accounting for the specific covariates 2. However, an ANOVA model (i.e., the same model as AH but without the covariates), show that the relation between suicide rate and nine-enders is non-significant. The authors estimate an ANCOVA model accounting for specific covariates (region, age, and total deaths) and find empirical support for the expectation. In Study 4, the authors study suicide victims across the United States between 20 and examine whether nine-enders are more likely to commit suicide. The Robustness of the Findings in Study 4 and 5 Hence, on the basis of the evidence presented by AH, the conclusion that people are more likely to start seeking extramarital affairs when they are nine-enders has notable limitations. One should note that this criticism is unrelated to whether or not people self-report their real age when seeking extramarital affairs online, but in other words that a male aged 29 may have signed up at the dating site when he was younger, e.g., 27 years old. More specifically, examining differences in the age distribution do not enable us to draw strict inferences on the age distribution users had when they signed up at the extramarital affairs dating site, i.e., when they decided to engage in the meaning searching behavior. In this study, AH draw inferences of the key independent variable, i.e., nine-ending digits, but this raises concerns related to the validity of the measure. 17067) and found that nine-enders were overrepresented at the site. There were 952,176 nine-enders registered on the site” (p. Here the authors “categorized 8,077,820 male users, aged between 25 and 64 years, according to the final digit of their ages. In Study 3, the authors argue that nine-enders are more likely to seek extramarital affairs online. Who are the Nine-Enders? Content Validity in Study 3 Overall, contrary to the interpretation made by AH, there is no systematic evidence that nine-enders question the meaning of life significantly more (or less) often.ģ. Figures 1A1-A3 show the unstandardized effects of the nine-ender variable in the different models. Hence, I report the results using the original data from AH and the six waves available from WVS as of March 26th, 2015. It is not possible to get an identical sample as AH with the data available from WVS. In the data set available from WVS, which is updated after the authors wrote their manuscript, there are 61,148 respondents in the age range 25–64. To cross-validate this finding I applied data from all six waves of the WVS with similar measures (compared to one wave used by the authors) and estimated the nine-ender effect as a simple difference in means (as AH), in an ordered logistic regression (to take the ordinal nature of the dependent variable into account) and in a mixed effects model (to treat age as a random covariate).
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They conclude, using survey data from the World Values Survey (WVS), that “nine-enders reported questioning the meaning or purpose of life more than respondents whose ages ended in any other digit” (p. In Study 1, AH examine whether people having an age ending at nine (29, 39, etc.) is more likely, on average, to question the meaning of life on a four point scale. The authors note that the paper “demonstrates a striking pattern in human behavior.” In this commentary I use the empirical material from AH as well as additional data and argue that the patterns demonstrated by AH are open to alternative explanations and lack conclusive evidence 1. More specifically, the authors conclude on the basis of six studies, that “adults undertake a search for existential meaning when they approach a new decade in age (e.g., at ages 29, 39, 49, etc.)” (p. In a recent published article in the Proceedings of the National Academy of Sciences, Alter and Hershfield (2014) (abbreviated AH) argue that people are more likely to engage in meaning searching activities as they approach a new decade in chronological age. Previous research has documented that personal experiences can influence the sense of meaning in life ( Machell et al., 2015) and that people report higher levels of searching for meaning in their earlier life stages ( Steger et al., 2009). People differ in the extent to which they engage in the search for meaning in life ( Steger et al., 2008).