Long-term trends (1980-2017) in the N-pact factor of journals in personality psychology and individual differences research

Recent metascience investigations of the N-pact factor (NF; median sample size of studies published in a journal) have revealed NFs of merely about 100 in fields like social, sport, and exercise psychology. Journal NF has also been shown to correlate negatively with journal impact factors (JIF), implying that smaller studies appear in more prestigious journals. In this first long-term and largest NF analysis to date (3,699 articles coded), annual NFs of two personality psychology journals were tracked over 38 years since their inception in 1980. Overall NF was about 190, gradually increased over time, and within-journal NF-JIF correlations were positive. Online samples and articles featuring supplemental files presented larger NFs, whereas those involving student samples had smaller ones. Sample size distributions showed multimodality, and surplusses of even-numbered sample sizes and of those just beyond 100 were evident. An NF statement, accompanying authors’ submitted papers, is suggested.