Introduction
Individuals entering college often experience significant novel environmental changes (Kidwell, Reference Kidwell2005). Executive functions may be heavily relied upon during this period, due to colleges and/or universities being more intellectually demanding (McKee, Reference McKee2017) and requiring goal-oriented behavior (Ahrens et al., Reference Ahrens, Lee, Zweibruck, Tumanan, Larkin and Beck2019; Turkstra & Byom, Reference Turkstra and Byom2010). Executive function consists of various cognitive processes, including cognitive flexibility, visuospatial abilities, and semantic fluency (Bigelow & Agrawal, Reference Bigelow and Agrawal2015; Carvalho & Ready, Reference Carvalho and Ready2010; gray, Reference Gray2001); each critical for academic success (Goldstein & Naglieri, Reference Goldstein and Naglieri2014). College students often experience stressors in pursuit of academic success, and being able to efficiently navigate through these stressors is crucial (Karaman et al., Reference Karaman, Lerma, Vela and Watson2019; Hubbard et al., Reference Hubbard, Reohr, Tolcher and Downs2018). Thus, individual differences in a person’s personality traits may influence how the student modulates their executive functions (Murdock et al., Reference Murdock, Oddi and Bridgett2013).
The most consistently reported Big Five personality trait that is associated with executive function performance is neuroticism, with much of the scientific literature presenting a negative relationship (Crespo-Sanmiguel et al., Reference Crespo-Sanmiguel, Zapater-Fajarí, Garrido-Chaves, Hidalgo and Salvador2024; Saylik et al., Reference Saylik, Szameitat and Cheeta2018; Waggel et al., Reference Waggel, Lipnicki, Delbaere, Kochan, Draper, Andrews, Sachdev and Brodaty2015). In contrast, higher levels in some other personality traits (e.g., conscientiousness, agreeableness, and openness) are reported to be associated with better executive functioning task performance (Crow, Reference Crow2019; Mercuri & Holtzer, Reference Mercuri and Holtzer2021). Specifically, openness to experience is associated with better memory (Luchetti et al., Reference Luchetti, Terracciano, Stephan and Sutin2016), verbal fluency (Chapman et al., Reference Chapman, Benedict, Lin, Roy, Federoff and Mapstone2017), and cognitive flexibility (Murdock et al., Reference Murdock, Oddi and Bridgett2013) task performance. Similar positive findings were reported for conscientiousness when determining its association with visuospatial abilities in nonclinical samples (Carbone et al., Reference Carbone, Meneghetti and Borella2019; Sutin et al., Reference Sutin, Stephan, Damian, Luchetti, Strickhouser and Terracciano2019). Other researchers have argued conscientiousness’ positive association with executive function may be attributable to cognitive flexibility (Fleming et al., Reference Fleming, Heintzelman and Bartholow2016). In addition to conscientiousness, agreeableness seems to obtain a conceptual and behavioral overlap in executive functioning (Jensen-Campbell et al., Reference Jensen-Campbell, Rosselli, Workman, Santisi, Rios and Bojan2002; Kochanska et al., Reference Kochanska, Aksan, Penney and Doobay2007; Williams et al., Reference Williams, Suchy and Kraybill2010). Previous research also suggests that agreeableness has a positive association with working memory, a vital component of executive function (Waris et al., Reference Waris, Soveri, Lukasik, Lehtonen and Laine2018).
The personality trait extraversion reported mixed findings with executive function tenets. Specifically, research suggests extraversion has little to no association with working memory or cognitive flexibility (Crow, Reference Crow2019; Krieger et al., Reference Krieger, Amador-Campos and Guàrdia-Olmos2020). Researchers posit this relationship may not exist without extraversion having a modulating positive mood construct to aid in facilitating the relationship (Stafford et al., Reference Stafford, Ng, Moore and Bard2010). In contrast to the null or negative findings, experimental researchers suggest that extraversion may differentiate among executive functioning tasks as a function of complexity (Campbell et al., Reference Campbell, Davalos, McCabe and Troup2011). Extraversion’s positive association with cognitive flexibility task performance has also been reported (Herrmann & Wacker, Reference Herrmann and Wacker2021). These findings are supported by cross-sectional analyses suggesting extraversion has a positive relationship with working memory (Dubey et al., Reference Dubey, Singh and Srivastava2014). Yet, various outcomes on this relationship between extraversion and executive function performance show inconsistency in results (Campbell et al., Reference Campbell, Davalos, McCabe and Troup2011).
Overall, many of the studies that examine the relationship between personality traits and executive function task performance are conducted in older adults (Mercuri & Holtzer, Reference Mercuri and Holtzer2021) and in clinical samples (Snyder, Reference Snyder2013). Literature has also consistently found neuroticism as a risk factor for severe internalizing symptoms (Speed et al., Reference Speed, Hemani, Speed, Børglum and Østergaard2019; Vinograd et al., Reference Vinograd, Williams, Sun, Bobova, Wolitzky-Taylor, Vrshek-Schallhorn and Craske2020). Internalizing symptom severity has also been reported to be deleterious to executive function task performance, including semantic fluency (Krogh et al., Reference Krogh, Benros, Jørgensen, Vesterager, Elfving and Nordentoft2014), cognitive flexibility (Ajilchi & Nejati, Reference Ajilchi and Nejati2017), and visuospatial processing (Blanken et al., Reference Blanken, White, Mous, Basten, Muetzel, Jaddoe and Tiemeier2017). Previous research also posits that the personality trait and executive function relationship may be a function of younger age (Graham & Lachman, Reference Graham and Lachman2014), with various relationships persisting in undergraduates, but not older adults. Ultimately, the relationship between personality traits and executive function task performance is still controversial, as previous research also reports weak to no relationship between executive function components and extraversion (Segel-Karpas & Lachman, Reference Segel-Karpas and Lachman2018), conscientiousness (Waris et al., Reference Waris, Soveri, Lukasik, Lehtonen and Laine2018), agreeableness (Vaughan & Edwards, Reference Vaughan and Edwards2020), and openness (Schretlen et al., Reference Schretlen, van der Hulst, Pearlson and Gordon2010). Yet neuroticism has been consistently negatively associated with executive function task performance (Saylik et al., Reference Saylik, Szameitat and Cheeta2018).
Personality traits’ complex structure requires the activation and potential interaction between neurobehavioral mechanisms, including executive functions (Nikolasevic et al., Reference Nikolašević, Krstić, Rajšli and Bugarski Ignjatović2024). Previous research posits personality traits are relied upon executive function (Forbes et al., Reference Forbes, Poore, Krueger, Barbey, Solomon and Grafman2014). Personality traits are comprised of constructs (e.g., goal-oriented behavior, impulsivity) that have direct executive functioning parallels. Much of the scientific literature reports findings on selected personality traits’ associations with executive functions (Campbell et al., Reference Campbell, Davalos, McCabe and Troup2011; Fleming et al., Reference Fleming, Heintzelman and Bartholow2016; Ihle et al., Reference Ihle, Zuber, Gouveia, Gouveia, Mella, Desrichard and Kliegel2019). However, very few studies have examined the associations among all of the Big Five personality traits and objective executive function task performance. The purpose of the current study is to determine associations between personality traits and executive function task performance among undergraduate college students. We hypothesize positive associations between some personality traits (i.e., conscientiousness, openness, extraversion, and agreeableness) and cognitive flexibility, semantic fluency, and visuospatial task performance. Additionally, we expected neuroticism to have a negative association with each executive function task performance.
Method
Participants
Participants in the current study consisted of undergraduate students from a historically Black university in central Virginia from the parent study entitled, “The Neuropsych Study” (Keen et al., Reference Keen, George, Williams, Blanden and Ramirez2022). Undergraduate students were recruited from the Psychology, Mathematics, Engineering, and Biology departments. The participants’ ages ranged between 18 and 47 years, with a mean age of 21.11 (standard deviation = 4.51) years. There were a total of 200 participants, including 146 females and 54 males. In order to participate in the current study, participants had to be undergraduate students and self-report a history of no traumatic brain injury during their lifetime. This study received annual approval from Virginia State University’s Institutional Review Board. The presented research was conducted in compliance with the Helsinki Declaration (Rickham, Reference Rickham1964).
Procedure
The current study’s procedure consisted of a one-time administration visit, which lasted approximately 45 minutes. Upon participant’s entry into the laboratory, a trained research assistant obtained informed consent. After informed consent was received, participants completed a series of questionnaires including a demographic questionnaire. We then administered a series of psychological assessments, which included the Trail Making Test (TMTA, TMTB, and TMTB-A) and Semantic Fluency (Semantic Fluency-Animals, Semantic Fluency-Vegetables, and Semantic Fluency-Fruits). Upon completion, participants’ names were sent to professors to receive extra credit in an undergraduate class.
Measures
Big Five inventory
The personality traits were measured using the Big Five Inventory (BFI; John et al., Reference John, Donahue and Kentle1991). The BFI was a 44-item self-report measure that assessed each big five trait from the Five-Factor Model of Personality (Costa & McCrae, Reference Costa and McCrae1999): openness to experience (10 items), conscientiousness (9 items), extraversion (8 items), agreeableness (9 items), and neuroticism (8 items). Participants responded to each of the items on a scale of 1 (strongly disagree) to 5 (strongly agree). Each personality trait scale was averaged. The higher scores represent stronger personality traits.
The Trail Making Test
The Trail Making Test (TMT-A and TMT-B) is a timed assessment measuring visuospatial tracking, set-shifting, and cognitive flexibility, among other executive function components. The TMT administration took approximately 5–10 minutes, with the objective requiring participants to connect numbers and/or letters in sequential order without lifting their pencils off the paper (Reitan, Reference Reitan1956). TMT-A consisted of only numbers and the TMT-B consisted of numbers and letters. Additionally, TMT-A subtracted from TMT-B yielded the TMTB-A score, which measures cognitive flexibility (Corrigan & Hinkeldey, Reference Corrigan and Hinkeldey1987). Scoring for the TMT was based on time lapsed, with higher scores indicating poorer performance.
Semantic fluency
Semantic Fluency is a neuropsychological assessment that measures memory recall, vocabulary, working memory, and fluid intelligence (Benton & Hamsher, Reference Benton and Hamsher1976). This measure takes approximately five (5) minutes to administer. Each item requires the participant to name words or objects that fit the given category. The measure categories were animals, vegetables, and fruits. All animals could be scored as correct for the animal category/type. Names such as “dog” and “cat” were accepted as canines and felines. Other generic domesticated terms like “cow” were also accepted. Each point indicated one accepted response. For vegetables and fruits, one correct response (being any fruit or vegetable depending on the task) was given one point. Total points were summed at the end of the 60 seconds for the final score.
Covariates
Demographic form
The demographic form was developed to collect general information about the participants. The form inquired about the participant’s age, biological sex, years of education, and employment status. Sex was dummy-coded as “0” for females and “1” for males. Employment status was dummy-coded as “0” for no current job, “1” for part-time job, “2” for full-time employment, and “3” for retired. Years of education were counted as the number of years the participant has been in school, beginning with the first grade.
Beck Depression Inventory-II
The Beck Depression Inventory (BDI-II) was used to determine depressive symptom severity. The BDI-II is a self-report scale used to measure internalizing symptoms such as appetite changes, sleep changes, sad mood, hopelessness, helplessness, suicidal ideations, and attention difficulties in adults. The BDI-II consists of 21 statements and responses ranging from 0 to 3, based on which response is most relatable to the individual. Statements such as, “I do not expect things to work out for me.”, “I dislike myself.”, and “I am so sad or unhappy that I can’t stand it.”. Scores of 0 to 13 indicate minimal depressive symptoms, 14 to 19 indicate mild, 20 to 28 are moderate depressive symptoms, and scores above 29 indicate severe depressive symptoms (Beck et al., Reference Beck, Steer and Brown1996). This measure has been used in Black/African American samples (Keen et al., Reference Keen, Turner, Mwendwa, Callender and Campbell2015; Keen et al., Reference Keen, Tan and Abbate2020) and has been reported to have an association with both personality traits (Buhan et al., Reference Buhan, Rehman and Keat2017; Perkovic & Pechenkov, Reference Perkovic and Pechenkov2023) and executive function (Klojčnik et al., Reference Klojčnik, Kavcic and Bakracevic Vukman2017). This measure was administered due to the parent study entitled, “The Neuropsych Study,” which sought to determine the association of depressive symptoms and executive function.
Data analysis
Data were analyzed using Statistical Package for Social Sciences, version 27 (IBM, 2020). Continuous variables were presented as mean (standard deviation). Frequencies and percentages were utilized for categorical variables. Pearson r correlations were employed to determine the association between demographic covariates, depressive symptoms, personality trait scores, and executive functioning measures. The demographic variables age, sex, years of education, employment, and depressive symptoms were treated as covariates in the regression analyses to address the study hypotheses. The primary predictors were extraversion, agreeableness, conscientiousness, neuroticism, and openness scales. Confidence intervals were reported for each predictor as effect sizes (Lee, Reference Lee2016). A sensitivity analysis conducted in G*Power version 3.1.9.7 (Erdfelder et al., Reference Erdfelder, Faul and Buchner1996) for N = 200 and five predictors revealed our sample was able to reliably estimate models with R 2 = 0.01 or greater at 80% power. Similarly, our sample was powered to detect zero-order correlations of r = 0.19 or above at 80% power.
Results
Descriptive
This current study consisted of 200 undergraduate students at a historically Black university. One hundred forty-six (73%) of those participants were female. Participants’ mean age was 21.11 (SD = 4.52). The majority of the sample was either unemployed (47%) or had a part-time job (41%). These results and others can be found in Table 1.
Table 1. Descriptive statistics
Note: BDI Total Score = Beck Depression Inventory Total Score; TMTA = Trail Making Test Trial A; TMTB = Trail Making Test Trial B; TMTB-A = Trail Making Test Trial A Subtracted from Trial B.
Correlations
Zero-order correlations were conducted between covariates, personality subscales, and executive functioning measures. Extraversion was negatively correlated with depressive symptoms. Agreeableness was negatively correlated with sex, depressive symptoms, and semantic fluency animals. Conscientiousness was positively correlated with age but negatively correlated with depressive symptoms and TMTA. Neuroticism was negatively correlated with sex but positively correlated with depressive symptoms. Openness was not statistically significant. These results and others can be found in Table 2.
Table 2. Correlations among neuropsychological scores, personality traits, and demographic variables
Zero-order correlations between demographic, depressive symptoms, big five personality traits, and executive function.
Note: **= p < .01; *= p < .05; Edu = Years of Education; Emp = Employment; BDI = Beck Depression Inventory; TMTA = Trail Making Test A; TMTB = Trail Making Test B; TMTB-A =Trail Making Test B-A; SF-A = Semantic Fluency Animals; SF-V = Semantic Fluency Vegetables; SF-F = Semantic Fluency Fruit; Extra = Extraversion; Agree= Agreeableness; Consci = Conscientiousness; Neuro = Neuroticism; Open = Openness.
Regression
Multiple regression analyses were employed to determine the associations between personality traits and executive function task performance in the presence of age, sex, education, employment, and depressive symptom covariates. Regression findings suggest conscientiousness was unexpectedly negatively associated with TMTA (β = −0.193, p = 0.017) but positively associated with TMTB-A (β = 0.197, p = 0.016). Openness was positively associated with TMTA (β = 0.166, p = 0.029), which was expected from our hypothesis. Agreeableness was also negatively associated with Semantic Fluency-Animals (β = −0.310, p < 0.001) and Semantic Fluency-Fruits (β = −0.215, p = 0.007), this was unexpected from our hypothesis. Neuroticism was negatively associated with Semantic Fluency-Vegetables (β = −0.268, p = 0.005), which supported our hypothesis. These results and others can be found in Tables 3 and 4. Scatter plots for each regression can be seen in Supplemental Materials labeled Figure 1.
Table 3. Trail making test regressed on personality traits and demographic covariates
Multivariate regression between demographic, depressive symptoms, big five personality traits, and executive function.
Note: TMTA = Trail Making Test Trial A; TMTB = Trail Making Test Trial B; TMTB-A = Trail Making Test Trial A subtracted from B; BDI = Beck Depressive Inventory; ** = p < 0.01; * = p < 0.05.
Table 4. Semantic fluency task regressed on personality traits and demographic covariates
Multivariate regression between demographic, depressive symptoms, big five personality traits, and executive function.
Note: SF = Semantic Fluency; BDI = Beck Depressive Inventory; ** = p < 0.01; * = p < 0.05.
Discussion
The current study sought to determine the association between personality traits and executive function task performance in undergraduate students. Agreeableness was negatively associated with two Semantic Fluency tasks, which was contrary to the study hypothesis. Openness was positively associated with TMTA, which was expected. Neuroticism was negatively associated with one Semantic Fluency task, which was consistent with previous literature (Sutin et al., Reference Sutin, Stephan, Damian, Luchetti, Strickhouser and Terracciano2019). Additionally, conscientiousness was negatively associated with TMTA but was positively associated with TMTB-A. This unexpected finding between conscientiousness and measures that focus on different types of executive function constructs (e.g., cognitive flexibility vs. visuospatial) may speak to both the healthy and deleterious influences of conscientiousness (Douglas et al., Reference Douglas, Cunningham, Tisdell and Arneson2023).
Previous research suggests cortical-related activity is associated with personality traits (Altinok et al., Reference Altinok, Rajkumar, Nießen, Sbaihat, Kersey, Shah, Veselinović and Neuner2021). Specifically, agreeableness is positively associated with the Default Mode Network (Sampaio et al., Reference Sampaio, Soares, Coutinho, Sousa and Gonçalves2014). Reportedly the Default Mode Network can become inactive when the individual is asked to perform cognitively demanding tasks (Crittenden et al., Reference Crittenden, Mitchell and Duncan2015), which may account for agreeableness’ negative association with semantic fluency in the current study. Further, Neuroticism is negatively associated with the left superior temporal gyrus activity (Lin et al., Reference Lin, Li, Pan, Liu, Zhang, Suo and Gong2023), an area associated with auditory processing and language (Bigler et al., Reference Bigler, Mortensen, Neeley, Ozonoff, Krasny, Johnson, Lu, Provencal, McMahon and Lainhart2007). These functions are also required in the semantic fluency tasks (Gaillard et al., Reference Gaillard, Sachs, Whitnah, Ahmad, Balsamo, Petrella and Grandin2003). Openness has been positively associated with the attentional networks, these same functions are required for the TMTA (Wang et al., Reference Wang, Zhuang, Li and Qiu2022), and in line with the positive association between visuospatial task performance and openness in the current study. Consistent with our findings, the anterior cingulate activity is negatively associated with visuospatial memory is also negatively associated with conscientiousness (Teixeira et al., Reference Teixeira, Pomedli, Maei, Kee and Frankland2006). The positive association between conscientiousness and more complex executive function tasks (cognitive flexibility) also aligns with previous activity-related findings. Specifically, conscientiousness is positively associated with activity in the lateral prefrontal cortex; an area involved in planning and cognitive flexibility (Tanji & Hoshi, Reference Tanji and Hoshi2008). In turn could further elucidate why conscientiousness was positively correlated with TMTB-A, as this measure assesses cognitive flexibility (Wang et al., Reference Wang, Zhuang, Li and Qiu2022). This empirical literature suggests neuroanatomical overlap between personality traits and executive function (Forbes et al., Reference Forbes, Poore, Krueger, Barbey, Solomon and Grafman2014), providing neurobehavioral explanations for associations reported in the current study.
Few studies have reported a negative association between conscientiousness and executive function task performance (Waris et al., Reference Waris, Soveri, Lukasik, Lehtonen and Laine2018). Waris et al (Reference Waris, Soveri, Lukasik, Lehtonen and Laine2018) identified this relationship with working memory, a key executive function component. In line with the limited findings in the literature, the current study also reports a negative association with consciousness between a task that includes attention, visual scanning, and visual perception. Previous research posits high levels of conscientiousness may also include obsessive-compulsive symptomatology and have adverse effects on an individual’s psychological health (Samuel & Widiger, Reference Samuel and Widiger2011; Carter et al., Reference Carter, Guan, Maples, Williamson and Miller2016).
Previous literature suggests that age may also be positively associated with conscientiousness levels (Soubelet, Reference Soubelet2011). Individuals with better executive function task performance reported higher conscientiousness levels in an older adult sample (Baker & Bischel, Reference Baker and Bichsel2006). Yet, in a study using adolescents, conscientiousness was negatively associated with short-term memory (Pearman, Reference Pearman2009). Specifically, the less complex task (visuospatial) held a negative relationship while the more complex executive function (cognitive flexibility) was positively associated with conscientiousness. These findings paired with the positive association between age and conscientiousness may reflect the usage of developmental heuristics in decision-making and other complex executive functions (Strough et al., Reference Strough, Karns and Schlosnagle2011). Future research should look to isolate executive function subtypes to help identify which may serve as behavioral or health-related mechanisms. There are positive and negative health effects across the executive function performance spectrum, and this relationship may vary or be heavily influenced by conscientiousness (Hall & Fong, Reference Hall and Fong2013).
Previous research suggests that openness is positively associated with executive function task performance (Schretlen et al., Reference Schretlen, van der Hulst, Pearlson and Gordon2010). The current findings support this literature, openness was positively associated with visuospatial skills (TMTA). Literature also suggests that openness allows the individual to be open to more stimulating experiences that provide learning opportunities which results in improving cognitive ability levels (Chamorro-Premuzic & Furnham, Reference Chamorro-Premuzic and Furnham2004; Ihle et al., Reference Ihle, Zuber, Gouveia, Gouveia, Mella, Desrichard and Kliegel2019). This positive relationship was not statistically significant until demographic, and other personality traits were statistically accounted for in the same model, leaving the potential for a modulating mechanism within covariates. Overall, higher levels of openness invoke more opportunities to further improve executive function skills, resulting in higher executive function performance.
Much literature suggests agreeableness is positively associated with semantic fluency (Sutin et al., Reference Sutin, Stephan, Damian, Luchetti, Strickhouser and Terracciano2019), visuospatial function (Sutin et al, Reference Sutin, Stephan, Damian, Luchetti, Strickhouser and Terracciano2019), and cognitive flexibility (Lange & Dewitte, Reference Lange and Dewitte2019). However, the negative association between agreeableness and executive function task performance is also supported by previous research (Byrne et al., Reference Byrne, Silasi-Mansat and Worthy2015). Byrne and colleagues suggest this negative relationship can be due to social pressure and possible test anxiety. Further, individuals who are more agreeable may have problems making decisions or fear others’ judgment. Problems with agreeableness may present themselves as internalizing symptoms (Flory et al., Reference Flory, Lynam, Milich, Leukefeld and Clayton2002). These symptoms are typically behaviors or feelings that are negatively slanted toward the individual, by the individual.
In the present study, neuroticism was positively correlated with depressive symptoms, which supports previous research; on internalizing symptomatology, specifically severe depressive and anxious symptoms (Muris et al., Reference Muris, Roelofs, Rassin, Franken and Mayer2005; Yoon et al., Reference Yoon, Maltby and Joormann2013). Depression has been known to negatively affect aspects of executive function (Friedman et al., Reference Friedman, du Pont, Corley and Hewitt2018). Individuals with higher neuroticism scores become more at risk for depressive symptoms, and this association may also influence executive function. This notion is further supported in our findings of neuroticism’s negative association with Semantic Fluency. However, neuroticism was not associated with all semantic fluency tasks, which could speak to the wider variance with the specific topic of vegetables compared to the other subtests. Ultimately, neurotic and internalizing symptoms may disrupt organic and behavioral processes that facilitate efficient executive function activity (Chapman et al., 2012).
There are limitations that should be noted within the study. First, the participant pool consisted of only undergraduate students and cannot be generalized to other non-collegiate individuals within a similar age range. This study recruited participants from only one college within the university, excluding others on the university’s campus. Given the cross-sectional nature of the study, we are unable to determine causality and may be underpowered to detect the expected effects. A longitudinal study design would allow for causal-based modeling for known covariates (i.e., depressive symptoms). This dataset did not contain objective measures to assess and then exclude learning disabilities, psychiatric history, ADHD, etc. This cross-sectional study did not allow us to use depressive symptoms as a mediator or moderator for our analyses.
In conclusion, our current study identified known (i.e., neuroticism) and rarely reported (negative associations with conscientiousness) associations between personality traits and executive function in a sample of undergraduate students. College students utilize executive function latent self-regulation in their daily lives (Cohen, Reference Cohen2012). As undergraduate students engage with their social environments, personality traits may modulate their perception and responsiveness to social stimuli (Robinson, Reference Robinson2007). Employing interventions that utilize personality trait targets (e.g., conscientiousness and neuroticism) may be a unique way to tailor cognitive training and performance (Studer-Luethi et al., Reference Studer-Luethi, Jaeggi, Buschkuehl and Perrig2012).
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S135561772400047X.
Acknowledgements
The first and third author were supported by a Research Enhancement Award (1R15 DA052886-01A1 and 3R15DA052886-01A1S1) from the National Institute on Drug Abuse. The funding sources had no role in the design, conduct, or analysis of the study, or in the decision to submit the manuscript for publication. Data was not preregistered in an independent institutional registry. The contents herein are solely the responsibility of the authors and do not necessarily represent the official views of the National Institute on Drug Abuse or the National Institutes of Health.
Author contribution
The first author led the data collection, manuscript conceptualization, formal analysis, and overall writing of the manuscript. The second author supported efforts relating to manuscript conceptualization, manuscript review, and editing.
Competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have influenced the results reported in this manuscript.
