Infrequent count data in psychological research are commonly modelled using zero-inflated Poisson regression. This model can be viewed as a latent mixture of an "always-zero" component and a Poisson component. Hurdle models are an alternative class of two-component models that are seldom used in psychological research, but clearly separate the zero counts and the non-zero counts by using a left-truncated count model for the latter. In this tutorial we revisit both classes of models, and discuss model comparisons and the interpretation of their parameters. As illustrated with an example from relational psychology, both types of models can easily be fitted using the R-package pscl.

The actor–partner interdependence model (APIM) has been widely used for the analysis of pairs of individuals who interact with each other. The goal of this article is to detail in a nontechnical way how the APIM for binary or count outcomes can be implemented and how actor and partner effects can be estimated using generalized estimating equations (GEE) methodology. Both SPSS‐ and SAS‐syntax needed to estimate the model and the interpretation of the output are illustrated using data from a study exploring the effect of satisfaction with the relationship before the breakup on unwanted pursuit behavior after the breakup in formerly married partners. The use of this GEE method will allow researchers to test a wide array of research hypotheses.

:  Former partners comprise the most important subgroup of stalkers. However, contextual factors related to the breakup are hardly examined to explain ex‐partner pursuit. In a community sample of 194 separated persons, about one‐fifth perpetrated at least one unwanted pursuit behavior in the past 2 weeks. Being female, lowly educated, and socially undesirable raised the number of perpetrated behaviors. Beyond these effects, the number of behaviors increased when the cause of the break was attributed to the ex‐partner or external factors and when the ex was appraised as the breakup initiator. Breakup reasons, the ex‐partner’s lack in meeting family obligations and own infidelity, also related to pursuit behaviors albeit inferior to subjective attributions and appraisals of initiation. Finally, participants who felt more anxious or lonely negative showed more behaviors. The results enlighten that the breakup context gains further attention. Clinical treatment might benefit from fostering cognitive reconstructions and breakup adjustment.

In the social sciences, mediation analysis has typically been formulated in the context of linear models using the Baron & Kenny (1986) approach. Extensions to nonlinear models have been considered but lack formal justification. By placing mediation analysis within the counterfactual framework of causal inference one can define causal mediation effects in a way that is not tied to a specific statistical model and identify them under certain no unmeasured confounding assumptions. Corresponding estimation procedures using parametric or nonparametric models, based on the so-called mediation formula, have recently been proposed in the psychological literature and made accessible through the R-package mediation. A number of limitations of the latter approach are discussed and a more flexible approach using natural effects models is proposed as an alternative. The latter builds on the same counterfactual framework but enables interpretable and parsimonious modeling of direct and mediated effects and facilitates tests of hypotheses that would otherwise be difficult or impossible to test. We illustrate the approach in a study of individuals who ended a romantic relationship and explore whether the effect of attachment anxiety during the relationship on unwanted pursuit behavior after the breakup is mediated by negative affect during the breakup.

This study investigated unwanted pursuit behavior (UPB) perpetration in 631 adult expartners. UPB involves the unwanted pursuit of intimacy, a widespread and usually less severe form of stalking. The occurrence and various risk factors of UPB perpetration were examined, accounting for differences between male and female ex-partners and same-and opposite-gender ex-partners. Ex-partners showed on average five to six UPBs after their separation. Male and female and same-and opposite-gender ex-partners displayed an equal number of UPBs. The number of perpetrated UPBs was explained by breakup characteristics (ex-partner initiation of the breakup and rumination or cognitive preoccupation with the expartner), relationship characteristics (anxious attachment in the former relationship), and individual perpetrator characteristics (borderline traits and past delinquent behaviors).Rumination was a stronger predictor in female than male ex-partners. Borderline traits and anxious attachment positively predicted UPB perpetration in opposite-gender but not in samegender ex-partners. Implications of these findings are discussed.

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This study re-examined the role of romantic relationship characteristics in unwanted pursuit behavior (UPB) perpetration. Relationship characteristics were investigated accounting for the role of significant breakup characteristics, using data of 396 legally divorced adults and advanced count regressions. Except conflict, the main effects of characteristics of the former relationship didn't contribute explained variance to the frequency of UPBs when controlling for the effects of significant breakup characteristics (initiator status and post-breakup negative affect). However, moderator analyses--investigating the interactions between relationship and breakup characteristics--did reveal significant effects of relationship satisfaction, alternatives, investments, and anxious attachment in interaction with initiator status and of relationship alternatives in interaction with post-breakup negative affect. These findings illustrate that the association between relationship characteristics and UPB perpetration is more complex than previously thought and are theoretically and clinically valuable. This resulted from the conceptualization of most stalking as a form of unwanted relationship pursuit as well as observations that stalking most often occurs between people with a shared relationship history (Spitzberg & Cupach, 2003). Cupach and Spitzberg (1998) elaborated on unwanted pursuit, which they named obsessive relational intrusion (ORI) and defined as "repeated and unwanted pursuit and invasion of one's sense of physical or symbolic privacy by another person, either stranger or acquaintance, who desires and/or presumes an intimate relationship" (pp. 234-235). Other researchers similarly developed constructs to describe these relational intrusions; for example, UPB (Langhinrichsen-Rohling et al., 2000), breakup persistence (Williams & Frieze, 2005), and intrusive contact (Haugaard & Seri, 2003).According to recent meta-analyses (Cupach & Spitzberg, 2004; Spitzberg & Cupach, 2007), the diversity of pursuit tactics can be classified into several categories. These cover a broad continuum of activities, starting from relatively mild behaviors and escalating in terms of severity, frequency, duration, and impact (e.g., Langhinrichsen-Rohling et al., 2000). By most judicial definitions, stalking occurs at the point when UPBs develop into an intentional pattern of repeated behaviors that result in fear or threat. Further, whereas UPBs exclusively result from a desire for intimacy with someone who is reluctant to engage romantically with the pursuer, stalking can also evolve from other motives such as hatred or revenge (Cupach & Spitzberg, 1998, 2004 Spitzberg & Cupach, 2007).Former partners have often been targeted in stalking and UPB studies because they represent the largest group of stalkers and pursuers (about 50%; for reviews, see Douglas & Dutton, 2001; Spitzberg & Cupach, 2007) and hold a higher risk for violent, persistent, and Post-Breakup Unwanted Pursuit 4 recurrent stalking behavior (for a review, s...