Coosje Veldkamp

Coosje Veldkamp
Amsterdam University Medical Center | VUmc · EMGO Institute for Health and Care Research

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19
Publications
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1,270
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Publications

Publications (19)
Article
Full-text available
Researchers face many, often seemingly arbitrary, choices in formulating hypotheses, designing protocols, collecting data, analyzing data, and reporting results. Opportunistic use of “researcher degrees of freedom” aimed at obtaining statistical significance increases the likelihood of obtaining and publishing false-positive results and overestimat...
Article
Full-text available
In this preregistered study, we investigated whether the statistical power of a study is higher when researchers are asked to make a formal power analysis before collecting data. We compared the sample size descriptions from two sources: (i) a sample of pre-registrations created according to the guidelines for the Center for Open Science Preregistr...
Article
Full-text available
In this paper, we present three retrospective observational studies that investigate the relation between data sharing and statistical reporting inconsistencies. Previous research found that reluctance to share data was related to a higher prevalence of statistical errors, often in the direction of statistical significance (Wicherts, Bakker, & Mole...
Article
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A survey in the United States revealed that an alarmingly large percentage of university psychologists admitted having used questionable research practices that can contaminate the research literature with false positive and biased findings. We conducted a replication of this study among Italian research psychologists to investigate whether these f...
Article
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Do lay people and scientists themselves recognize that scientists are human and therefore prone to human fallibilities such as error, bias, and even dishonesty? In a series of three experimental studies and one correlational study (total N = 3,278) we found that the 'storybook image of the scientist' is pervasive: American lay people and scientists...
Article
Full-text available
The designing, collecting, analyzing, and reporting of psychological studies entail many choices that are often arbitrary. The opportunistic use of these so-called researcher degrees of freedom aimed at obtaining statistically significant results is problematic because it enhances the chances of false positive results and may inflate effect size es...
Article
Full-text available
Background: Personality influences decision making and ethical considerations. Its influence on the occurrence of research misbehavior has never been studied. This study aims to determine the association between personality traits and self-reported questionable research practices and research misconduct. We hypothesized that narcissistic, Machiave...
Data
Invitational Email (Text A). Questionnaires included in the electronic survey (Text B). (DOCX)
Data
Exponentiated regression coefficients Exp(beta) for linear regression of RMSS on personality traits and results of tests effect modification by PPQ and academic position (to clarify the beta scores: an increase of 1 standard deviation in Machiavellianism is associated with an increase of 12% in the geometric mean of RMSS+1). (DOCX)
Data
Table with subanalysis of RMSS = 0. (DOCX)
Data
Proportion of variance in outcome measure explained by the models. (DOCX)
Article
Full-text available
Replication is often viewed as the demarcation between science and nonscience. However, contrary to the commonly held view, we show that in the current (selective) publication system replications may increase bias in effect size estimates. Specifically, we examine the effect of replication on bias in estimated population effect size as a function o...
Article
Full-text available
We respond to the commentaries Waldman and Lilienfeld (Psychometrika, 2015) and Wigboldus and Dotch (Psychometrika, 2015) provided in response to Sijtsma's (Sijtsma in Psychometrika, 2015) discussion article on questionable research practices. Specifically, we discuss the fear of an increased dichotomy between substantive and statistical aspects of...
Article
Full-text available
Statistical analysis is error prone. A best practice for researchers using statistics would therefore be to share data among co-authors, allowing double-checking of executed tasks just as co-pilots do in aviation. To document the extent to which this 'co-piloting' currently occurs in psychology, we surveyed the authors of 697 articles published in...

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