Subject Pool Research Articles

Extraction of canine gait characteristics using a mobile gait analysis system based on inertial measurement units

This study aims to investigate two simple algorithms for extracting gait features from an inertial measurement unit (IMU) based canine gait analysis system. The first algorithm was developed to determine the hip/shoulder extension/flexion range of motion. The second algorithm automatically determines the stance and swing phase per leg. To investigate the accuracy of the algorithms, two dogs were walked on a treadmill and measured simultaneously with an IMU system, an optical tracking system and two cameras. The range of motion estimation was compared to the optical tracking systems, with a total of 280 steps recorded. To test the stance and swing phase detection, a total of 63 steps were manually annotated in the video recordings and compared with the output of the algorithm.The IMU's-based estimation of the range of motion showed an average deviation of 1.4° to 5.6° from the optical reference, while the average deviation in the detection of the beginning and end of the stance and swing phases ranged from -0.01 to 0.09 s. This study shows that even simple algorithms can extract relevant information from inertial measurements that are comparable to results from more complex approaches. However, additional studies including a wider subject pool need to be conducted to investigate the significance of the presented findings.

A brief web-based depression literacy, efficacy, and stigma intervention among college students

ABSTRACT Objective The purpose of this study was to examine the impact of a brief web-based depression literacy intervention compared to a control condition on depression literacy, depression literacy efficacy, self-stigma, perceived public stigma, and personal stigma toward depression. Method College students (N = 210) from a large university in the southeastern United States were recruited via a human subject pool and randomly assigned to the intervention (web-based depression literacy) or control condition. Participants completed online surveys at pre-intervention, post-intervention, and 1-month follow-up time points. A short qualitative reflection question was also responded to post-intervention. Results No significant intervention condition by time interactions were seen across any variables included in the study. Significant main effects of time were found for the depression literacy, depression literacy efficacy, self-stigma, and personal stigma variables. Qualitative results show participants reported gaining a general understanding of depression in addition to more specific information such as knowing different treatment options or depression related resources. Discussion Education through a brief web-based depression literacy intervention did not improve college students’ literacy, confidence in recognising, managing, and preventing depression, or stigma towards this mental health disorder, compared to an active control condition.

Investigating gender-based differential item functioning on the McLean Screening Instrument for Borderline Personality Disorder (MSI-BPD): An item response theory analysis.

The McLean Screening Instrument for Borderline Personality Disorder (MSI-BPD) is a popular screening tool for identifying people who may have borderline personality disorder (BPD). However, because women are more frequently diagnosed with the disorder than men, it is possible that the MSI-BPD differs in its ability to identify BPD as a function of gender identity. Using item response theory (IRT), we sought to determine if components of the MSI-BPD would demonstrate differential item functioning (DIF), such that one gender identity would be more likely to endorse certain items. Twenty-two thousand thirty-five college undergraduates (14,305 women) aged 18-55 years (M = 18.77, SD = 1.75) were assessed using the MSI-BPD as part of a subject pool screening between 2008 and 2019. The MSI-BPD contains 10 items that are measured dichotomously, and the authors recommend a cut-off of 7 of 10 items endorsed to maximize sensitivity and specificity to BPD. Results suggested that a two-parameter model was the best fit to the data and that unidimensionality and local independence assumptions were met. The following items demonstrated DIF: self-harm/suicidality, affective lability, abandonment, impulsivity, and anger. At equal levels of the latent construct of BPD, women were more likely to endorse self-harm/suicidality, affective lability, and abandonment. Women were more likely to endorse impulsivity at higher levels of BPD, and men were more likely to endorse anger at lower levels of BPD. Ultimately, the effect sizes of these differences were small, however, and likely do not impact the individual's overall outcome on the measure. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Relationship between gait stability indices and gait parameters comprising joint angles based on walking data from 288 people.

Stability during walking is essential because falling accidents may lead to severe injuries. In this study, we calculated the margin of stability (MoS) and the maximum Lyapunov exponent (λs), which are two major stability indices for walking, using a gait database representing 300 healthy people. Previously, the relationships between these indices and other gait parameters, including joint angles, have not been investigated in such a large subject pool. Therefore, we determined the relationships between these stability indices and the gait parameters by calculating correlation coefficients and performing multiple regression analysis. The results indicated that MoS is dominated by walking speed in the forward direction and associated with various joint angles in the lateral direction. Conversely, no relationships were identified between λs and the gait parameters. Although both MoS and λs are considered as measures of gait stability, they are independent. The results of this study suggest that MoS and λs represent different aspects of gait motion.

Posttraumatic growth, purpose, and trauma in university survivors of sexual assault

Objective: This study focused on purpose as a key mechanism of posttraumatic growth for university student survivors of sexual assault. Participants: An online survey was completed by 278 participants of various ethnic, racial and gender backgrounds, recruited through email, social media, department subject pools, and Amazon Mechanical Turk. Methods: Researchers used mixed methods, concurrent triangulation approach in which quantitative and qualitative data were collected simultaneously with closed and open-ended questions. Results: Hierarchical multiple regression demonstrated that age, purpose in life, high magnitude stressors, and trauma history were significantly related to posttraumatic growth. Emergent themes described the impacts of sexual assault, how sexual assault impacts purpose, and ways in which purpose impacted posttraumatic growth. Conclusion: Results confirmed the association of purpose with posttraumatic growth as well as other key impacts of trauma that should be investigated further. Next steps include evaluating therapeutic interventions focused on purpose.

The effect of cognitive load on economic decision-making: a replication attempt

When cognitive load exceeds cognitive capacity, individuals may make poorer decisions, especially when substantial deliberation is required. Deck and Jahedi’s (2015) influential work on cognitive load found that individuals whose arithmetic performance is most impacted by high cognitive load become more risk averse, less patient and more subject to the anchoring effect. Since results of cognitive load manipulation studies are mixed, replication of influential studies is essential to strengthen our understanding of the effects of cognitive load. In this paper, we attempt to closely replicate Experiment 1 in Deck and Jahedi (2015). Though we observe similar effects of cognitive load on arithmetic performance, we fail to replicate their overall results on risky choice and impatience. While we are unable to clearly identify the reasons for this non-replication, the evidence points to subtle differences in the allocation of attention and effort across subject pools.

Aspirin-Dipyridamole in Fluctuating Small Vessel Disease Ischemic Strokes (P7-5.013)

<h3>Objective:</h3> Short-term inpatient use of aspirin-dipyridamole (Aggrenox) in small vessel disease (SVD) ischemic strokes (IS) may reduce neurologic fluctuations, leading to better functional outcomes. This single-center retrospective case-control study aims to compare outcomes in patients diagnosed with SVD IS who received Aggrenox versus standard antiplatelet therapy. <h3>Background:</h3> Aggrenox is a fixed-dose combination of aspirin, an antiplatelet, and extended-release dipyridamole, which acts both to impair platelet function and cause vasodilation. Previous studies showed Aggrenox to be safe and effective for secondary stroke prevention. We suspect that early use of Aggrenox could be effective for stroke prevention and functional outcomes due to its vasodilatory properties. <h3>Design/Methods:</h3> A retrospective analysis of patients diagnosed with SVD IS between January 2016–December 2020 was completed. We plan to enroll patients admitted through September 2022. Patients with age ≥18, who received a minimum of four doses of Aggrenox during hospitalization, will be matched with control patients who did not receive Aggrenox. Study end points include discharge NIHSS compared hospital day 1 and discharge mRS compared to admission. REDCap is being used for data collection and generation of descriptive statistics. <h3>Results:</h3> Thus far, 49 patients have qualified for inclusion into the Aggrenox cohort, with data collection still in progress. Subject pool has mean age 55; 49% male; 82% African American; 49% diabetic; 37% received tPA; mean length of time from admission to administration of Aggrenox of 26 hours; mean duration of Aggrenox 4 days; mean NIHSS on admission 5.7; mean NIHSS on discharge 5.1; mean mRS at admission 0.6; mean mRS at discharge 2.7; 41% of patients discharged home, 57% to inpatient rehabilitation, and 2% to a skilled nursing facility. <h3>Conclusions:</h3> Data in the Aggrenox population shows a trend toward improvement in NIHSS throughout hospitalization. Once control group data is collected, comparative statistics will be used to analyze outcomes between the two groups. <b>Disclosure:</b> Dr. Moran has nothing to disclose. Dr. March has nothing to disclose. Dr. Nearing has nothing to disclose.

Motivated beliefs, social preferences, and limited liability in financial decision-Making

We conduct a novel experiment to compare how subjects form motivated beliefs in an investor-client setup with varying degrees of liability. Although we do not detect the formation of motivated beliefs, our results indicate that social preferences significantly influence investment decisions and belief formation when investors have no liability. Once we limit our subject pool to those who display social preferences (i.e., those that donate more than zero in a dictator game), we find evidence of motivated belief formation. Additionally, we show that such motivated beliefs result in significantly higher investments. These findings highlight the importance of social preferences in financial decision-making and align with the recent literature on motivated belief formation under limited liability (Barberis, 2013; Bénabou and Tirole, 2016).

Trust and Strength of Family Ties: New Experimental Evidence

We provide a conceptual replication of an experimental study that uncovered a robust correlation between the strength of individuals’ family ties and their distrust of strangers, striving to establish whether the link is causal. Using a different subjects pool and an online setting, we repeat the binary trust-game experiment from Ermisch and Gambetta and enrich it by manipulating the payoffs to create a low-trust and high-trust environment. The key finding is corroborated, but as expected, only in the high-trust environment. The two environments further allow us to impose a diff-and-diff design on the data, which rules out selection of low-trusting individuals into strong-tied families and gives us indirect evidence of causation, namely, that having strong family ties stunts the development of trust in strangers. Our findings support the emancipatory theory of trust proposed by Toshio Yamagishi and could be interpreted as uncovering the micro foundations of classic ethnographic studies, such as that by Edward Banfield, which described how subcultures fostering tight bonds within families or small groups make cooperation harder to be achieved.

Construction and preliminary validation of an inconsistent responding scale for the HEXACO-100.

Inconsistent responding poses a particular risk to self-report data and is a common phenomenon in undergraduate and community subject pools. The HEXACO-100 personality inventory (Lee & Ashton, 2018) lacks internal validity scales that could be used to identify inconsistent responding. To address this need, the present study developed a HEXACO Inconsistent Responding Test (HIRT). Highly correlated and conceptually overlapping HEXACO-100 item pairs were identified from a derivation sample and cross-validated by comparing real data to randomly generated protocols. The HIRT was highly accurate at identifying both randomly generated and half-randomly generated protocols. HIRT scores exhibited significant correlations with other inconsistency measures (i.e., the Triarchic Assessment Procedure for Inconsistent Responding and the HEXACO's Inter-item Standard Deviation) and were as effective as these other measures at differentiating between consistent and inconsistent responders. This preliminary validation of the HIRT provides strong evidence of its ability to improve the quality of data gathered with the HEXACO-100, which may be especially useful for researchers hoping to utilize the measure in clinically relevant research and applications. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Three Layers of Uncertainty

Abstract We explore decision-making under uncertainty using a framework that decomposes uncertainty into three distinct layers: (1) risk, which entails inherent randomness within a given probability model; (2) model ambiguity, which entails uncertainty about the probability model to be used; and (3) model misspecification, which entails uncertainty about the presence of the correct probability model among the set of models considered. Using a new experimental design, we isolate and measure attitudes toward each layer separately. We conduct our experiment on three different subject pools and document the existence of a behavioral distinction between the three layers. In addition to providing new insights into the underlying processes behind ambiguity aversion, we provide the first empirical evidence of the role of model misspecification in decision-making under uncertainty.

Driver Attention Assessment Using Physiological Measures from EEG, ECG, and EDA Signals.

In this paper, we consider the evaluation of the mental attention state of individuals driving in a simulated environment. We tested a pool of subjects while driving on a highway and trying to overcome various obstacles placed along the course in both manual and autonomous driving scenarios. Most systems described in the literature use cameras to evaluate features such as blink rate and gaze direction. In this study, we instead analyse the subjects' Electrodermal activity (EDA) Skin Potential Response (SPR), their Electrocardiogram (ECG), and their Electroencephalogram (EEG). From these signals we extract a number of physiological measures, including eye blink rate and beta frequency band power from EEG, heart rate from ECG, and SPR features, then investigate their capability to assess the mental state and engagement level of the test subjects. In particular, and as confirmed by statistical tests, the signals reveal that in the manual scenario the subjects experienced a more challenged mental state and paid higher attention to driving tasks compared to the autonomous scenario. A different experiment in which subjects drove in three different setups, i.e., a manual driving scenario and two autonomous driving scenarios characterized by different vehicle settings, confirmed that manual driving is more mentally demanding than autonomous driving. Therefore, we can conclude that the proposed approach is an appropriate way to monitor driver attention.

Autobiographical memory and the self on the psychosis continuum: investigating their relationship with positive- and negative-like symptoms

ABSTRACT Autobiographical memory is severely impaired in schizophrenia, but previous work has largely treated both as unitary concepts. Here, we examined how various dimensions of autobiographical memory relate to different aspects of psychosis. Participants were recruited from the general population (Study 1, N = 264) and a university subject pool (Study 2, N = 305). We examined different measures of autobiographical memory and self (i.e., involuntary memory, autobiographical recollection, self-knowledge and self-awareness), at the trait level in Study 1 and both trait and state levels in Study 2, as a function of positive-and negative-like symptoms of psychosis. Across both studies, positive and negative dimensions of psychosis were found to be related to an increase in involuntary memories (i.e., the spontaneous recall of personal memories), and to lower self-concept clarity and insight. Positive and negative dimensions of psychosis correlated differently with autobiographical recollection characteristics, measured at both trait (Studies 1 and 2) and state levels (Study 2). Positive-like symptoms (in particular hallucination-proneness) showed a stronger and more consistent pattern of correlations than negative-like symptoms. These findings call for a dimensional approach to the relationship between autobiographical memory and psychosis symptoms in clinical and non-clinical individuals, to better understand the breakdown of autobiographical memory in the psychopathology of psychosis.

Subject confusion and task non-completion: Methodological insights from an artefactual field experiment with adolescents in India

In the behavioral and experimental economics literature, very few experiments measure and analyze subject confusion or the completion of laboratory tasks. In this paper, we examine pre-task quiz performance in our artefactual field experiment with an adolescent subject pool in India and find that females have a lower degree of confusion in comprehending task instructions as compared to males. Furthermore, economic status is negatively associated with subject comprehension and completion of incentivized experimental tasks. Academic ability is negatively associated with subject confusion and positively associated with task completion. Finally, we find a positive association between pre-task quiz performance and the completion of incentivized tasks. This suggests that unincentivized pre-task quiz scores may act as a signal for potential non-completion of incentivized tasks in experiments, particularly with non-standard subject pools.

Attitudes Toward Sexual Orientation and Gender Identity in Online Multiplayer Gaming Spaces.

Online video game communities can provide a sense of belonging and support for marginalized people, while at the same time, can be rife with prejudice and discrimination. This study aimed to assess the prevalence of both positive and negative comments about sexual orientation and gender identity during online gaming, and to test the hypothesis that LGBTQ+ people witness or experience more prejudice than do heterosexual and cisgender persons. An online survey, distributed on social media sites and a psychology subject pool, included rating scales and open-ended questions on game-related conversations. Respondents (N = 185) provided negative examples made by others more frequently than positive ones and attributed serious comments to themselves versus jokes and offhand comments to others. Across all respondent gender identities, the targets of the negative comments by others were almost always LGBTQ+ persons. These results bolster critiques of online gaming environments as hostile to members of marginalized groups.

Does climate change concern alter individual tax preferences? Evidence from an Italian survey

PurposeThis paper analyzes the role that the climate change concern (CCCi) has on the willingness to accept an environmental tax. The author aims to grasp how individual general tax preferences can differ with respect to the specific (environmental) tax. He focuses attention to the Italian case since it has been argued that the potential acceptability of a carbon tax in Italy is relatively high, and this topic has been scarcely explored so far among Italian citizens (Rotaris and Danielis, 2019).Design/methodology/approachThe author conducted an online survey among 514 Italian economics students.FindingsThe CCCi positively influences the environmental tax morale (ETMi). The general tax morale (TMi) positively affects the specific (environmental) TMi. The CCCi alters individual tax preferences. The author evidenced that also subjects with low TMi turned out to be willing to pay an environmental tax if aware of the environmental issues.Research limitations/implicationsAlthough the author used a common methodology in this strand of research, he is aware that in an online survey individuals can be influenced by the self-reporting and hypothetical choice bias (see Swamy et al., 2001), that in turn can characterize their reported preferences. Moreover, even if economics university students are commonly used as a subject pool in experimental economics settings, and although several studies showed that the behavioral responses of students are largely the same as those of nonstudents in identical experiments (for a discussion see Alm, 2012; Choo et al., 2016), there is awareness that in this case, they are not taxpayers yet (Barabas and Jerit, 2010).Practical implicationsThe author’s results remark the importance of increasing climate change awareness among people to let them be more willing to pay the environmental tax, for instance through investments in sensibilization campaigns on the importance of energy source usage and climate-related topic. Then, an increase in the general TMi leads to an increase in the specific (environmental) TMi. The author’s evidence showed that people with high tax morale logically recognize the positive impact of paying an environmental tax when the CCCi increases, since the more the theme becomes important, the larger the willingness to pay the specific tax. For this reason, policymakers should carry on campaigns to increase the general level of TMi to increase the overall tax compliance level and the relative tax revenues, following the guidelines given by the Organisation for Economic Co-operation and Development (2019) to support taxpayer education programs, such as including TMi research and analysis into education programs, improving the ease of paying taxes or strengthening revenue–expenditure links to build the social contract.Social implicationsIt should be paramount to increase awareness about environmental topics among people in general and among those who are relatively tax immoral. The author’s results remark on the importance of targeting energy and environmental tax policies to groups rather than to individuals. According to this evidence, we support the use of nonmonetary tools to nudge people in the environmental transition by changing their behavior in energy use, for instance through the taxation on fuel and other nonrenewable energy resources.Originality/valueIt is the first empirical study that analyzes the impact of CCCi on the environmental TMi in Italy, in particular controlling for the role of the general willingness to pay taxes (TMi). To obtain individual attitudes toward tax payment, most of the empirical studies in behavioral economics employ international surveys. For studies across citizens living in European countries, the European Social Survey (ESS) and European Values Study (EVS) represent the most used ones (see, for instance, Martinez-Vazquez and Torgler (2009) in Spain; Torgler and Werner (2005) in Germany; Nemore and Morone (2019) in Italy). However, these surveys do not allow to study the relationship between the environmental and general TMi across the same subject pool. In fact, despite the ESS (2016) provides individual responses about the willingness to pay an environmental tax, it does not provide information about the general individual attitude toward tax payment (this information is contained only in the ESS wave of 2004, hence referring to a different subject pool). On the contrary, each wave of the EVS (i.e. 2008, 2017) provides information about the general individual attitude toward tax payment, but this survey does not provide a question regarding the willingness to pay an environmental tax. Therefore, to obtain information about the willingness to pay both general and environmental taxes, across the same subject pool, it is needed to carry out a survey.

Pot at the End of the Rainbow: Cannabis Use Among Sexual Minorities.

Introduction: Gay, lesbian, and bisexual individuals (i.e., sexual minorities) use cannabis more frequently than heterosexuals; however, little research has directly compared sexual minorities' patterns of cannabis use (e.g., quantity, age of onset, forms of cannabis used) with heterosexuals. Some research has identified motivations for cannabis use in sexual minorities, but much of this research has been qualitative and/or narrow in scope (e.g., focused on sexual motivations). To the best of our knowledge, no previous research has used a validated measure to examine motives for cannabis use among sexual minorities. Additionally, cannabis use is known to be associated with mental health symptoms, but little research has examined relationships between cannabis use and mental health in this population. Materials and Methods: Data analyses were performed on archival survey data collected from 10 undergraduate psychology subject pools across the United States (N=4,669) as a part of Project ART (Addictions Research Team). Participants indicated their sexual orientation using a 5-point scale, and responses were used to classify participants into three groups: the majority of the sample (n=3,483) were classified into the heterosexual group, about one quarter were classified into the bisexual group (n=1,081), and a small number were classified into the gay group (n=105). Results: The bisexual group was more likely to report using cannabis. They also reported using cannabis more frequently, were more likely to report use of all product types (i.e., flower, concentrates, and edibles), and reported more severe symptoms of cannabis use disorder (CUD) than the heterosexual group. The bisexual group also reported higher levels of coping and enhancement motives for using cannabis and reported higher levels of all measured mental health symptoms (e.g., depression, suicidality, generalized anxiety, and social anxiety) compared with the heterosexual group. Conclusions: Increased frequency of cannabis use, use of a broad range of different products, and use of cannabis to cope with mental health concerns may be placing bisexual individuals at greater risk of CUD. Findings from this study can be used to guide future research and help target mental health interventions among bisexual individuals.

The Efficacy of Tadalafil and Tadalafil + Dapoxetine in Managing Sexual Dysfunction in Individuals with Type-2 Diabetes Mellitus

Objective: The present study was aimed to evaluate effect of metabolic parameters on erectile dysfunction (ED) in individuals with type-2 diabetes mellitus (T2DM) and to assess the efficacy of Tadalafil and Tadalafil + Dapoxetine combination. Materials and Methods: A prospective, observational, cross-sectional, bicentric study included 216 males with T2DM who are not treated with phosphodiesterase 5 inhibitors and without chronic kidney disease. The data were obtained from demographic questionnaire, clinical laboratory reports of glycometabolic parameters namely body mass index (BMI), hemoglobin A1c (HbA1c), testosterone, vitamin B12 (VitB12), and lipid profile and analyses of the International Index of Erectile Function (IIEF) questionnaire. The effect of physical and metabolic parameters on IIEF sub-domains namely erectile function; orgasmic function; sexual desire (SD); intercourse satisfaction; and overall satisfaction was evaluated. A statistical significance was evaluated using χ 2 test or t-test. Result: SD is most significantly lower in subjects with imbalanced physiological and metabolic characteristics including BMI, HbA1c, testosterone, VitB12, triglyceride, high-density lipoprotein, and low-density lipoprotein. Both Tadalafil and Tadalafil + Dapoxetine significantly improved almost all IIEF parameters without any pronounced effect of either. Similarly, both the treatments improved all the IIEF parameters for subjects with high BMI except for SD. In subjects with cardiac comorbidities, the use of either treatment significantly enhanced all the IIEF scores. Conclusion: The findings of this study outline the need of careful examination of sexual dysfunction in healthcare clinics for diabetic individuals. An imbalanced physiological and metabolic profile leads to ED in individuals with T2DM. Additionally, the presence of co-morbidities further elevates the odds of ED prevalence. The treatment with Tadalafil and Tadalafil + Dapoxetine drug combination shows promising results in improving the ED but a study with larger pool of subjects is needed to determine the additional benefits of Dapoxetine.

Framing and subject pool effects in healthcare credence goods

Credence goods markets are characterized by asymmetric information between experts and consumers, specifically relating to quality (what is needed and/or supplied). The functioning of the market is heavily reliant on trust on the side of the consumer and trustworthiness on the side of the expert. However, a large body of empirical and experimental research has demonstrated the existence of overtreatment, undertreatment, and overcharging in several credence goods markets. In this paper, we study two determinants of trust and trustworthiness in experimental credence goods markets: the effects of a health frame (vs. a neutral frame) and an expert subject pool (vs. standard student subject pool). Our results reveal that the subject pool, in combination with the health frame, has a significant impact on the level of trust and trustworthiness, shown by a higher willingness of consumers (patients) to enter the market and a lower rate of undertreatment by experts.

Group differences in binge eating, impulsivity, and intuitive and mindful eating among intermittent fasters and non-fasters

Intermittent fasting (IF) is an increasingly popular diet involving short-term fasting and/or caloric restriction. While published research highlights physiological effects (e.g., weight, body fat) of IF, hardly any research has examined its associations with psychological factors. This study aimed to investigate the relationship between IF and binge eating, impulsivity, intuitive eating, and mindful eating. An undergraduate sample (N = 298) was recruited through a large southwestern university psychology subject pool. The sample was divided into three groups based on IF status: Current IF (n = 70), Past IF (n = 48), and No IF (n = 182). Current IF was negatively associated with lack of perseverance (e.g., “I generally like to see things through to the end”; p < .01) and intuitive eating (p < .05), varying by subscale, compared to the other groups. Notably, Past-IF, but not Current IF, participants were more likely to binge eat than individuals who reported never fasting (p = .03). These findings add credence to the rapidly developing area of research suggesting IF is associated with increased disordered eating behaviors. Notably, the findings from this study are limited due to the lack of diversity sample, such that generalizations can only be made toward White, middle-to-high income, college students. Future longitudinal studies are needed to test the directionality of these relationships.