Conscientiousness and IQ

There seems to be little agreement amongst scientists on the relation between these factors:

• 2014 How are conscientiousness and cognitive ability related to one another? A re-examination of the intelligence compensation hypothesis - “true association between these constructs may be zero or positive at the population level but that the use of selected research samples has sometimes resulted in the appearance of a negative association.”

• 2006 Is conscientiousness positively or negatively related to intelligence? Insights from the national level - “Self-report conscientiousness scores are negatively associated with IQ” while “Observer-rated conscientiousness scores tend to positively correlate with IQ.”

• 2015 Why is Conscientiousness negatively correlated with intelligence? - “the negative relationship between intelligence and Conscientiousness is due to fluid intelligence affecting the development of Conscientiousness, in an educated and need-achieving population”

• 2014 The social influences on trait Conscientiousness: Findings from a nationally representative sample - “a significant, but very small positive association between intelligence, social factors and Conscientiousness.”

• 2023 Conscientiousness and Cognitive Abilities: a Meta-Analysis - “Several random-effects meta-analyses were conducted, obtaining meta-analytical correlations of .02, -.06 and -.06 between Conscientiousness (global) and cognitive abilities (global), crystallized intelligence and fluid intelligence, respectively.” Unclear why they exclude studies that do NOT “report any link between Conscientiousness and cognitive ability”, that seems like a “fail to reject the null hypothesis” result that should be very relevant?