The EM algorithm for latent class analysis with equality constraints

The EM algorithm is a popular iterative method for estimating parameters in the latent class model where at each step the unknown parameters can be estimated simply as weighted sums of some latent proportions. The algorithm may also be used when some parameters are constrained to equal given constants or each other. It is shown that in the general case with equality constraints, the EM algorithm is not simple to apply because a nonlinear equation has to be solved. This problem arises, mainly, when equality constrints are defined over probabilities indifferent combinations of variables and latent classes. A simple condition is given in which, although probabilities in different variable-latent class combinations are constrained to be equal, the EM algorithm is still simple to apply.The authors are grateful to the Editor and the anonymous reviewers for their helpful comments on an earlier draft of this paper. C. C. Clogg and R. Luijkx are also acknowledged for verifying our results with their computer programs MLLSA and LCAG, respectively.     

The integration of multidimensional scaling and multivariate analysis with optimal transformations

The recent history of multidimensional data analysis suggests two distinct traditions that have developed along quite different lines. In multidimensional scaling (MDS), the available data typically describe the relationships among a set of objects in terms of similarity/dissimilarity (or (pseudo-)distances). In multivariate analysis (MVA), data usually result from observation on a collection of variables over a common set of objects. This paper starts from a very general multidimensional scaling task, defined on distances between objects derived from one or more sets of multivariate data. Particular special cases of the general problem, following familiar notions from MVA, will be discussed that encompass a variety of analysis techniques, including the possible use of optimal variable transformation. Throughout, it will be noted how certain data analysis approaches are equivalent to familiar MVA solutions when particular problem specifications are combined with particular distance approximations.This research was supported by the Royal Netherlands Academy of Arts and Sciences (KNAW). An earlier version of this paper was written during a stay at McGill University in Montréal; this visit was supported by a travel grant from the Netherlands Organization for Scientific Research (NWO). I am grateful to Jim Ramsay and Willem Heiser for their encouragement and helpful suggestions, and to the Editor and referees for their constructive comments.     

Symptom patterns in late luteal-phase dysphoric disorder

The symptom patterns of 180 women with prospectively confirmed late luteal-phase dysphoric disorder (LLPDD) were examined using a careful application of factor and cluster analytic techniques. Factor analysis of premenstrual change scores on 33 common premenstrual syndrome symptoms yielded four orthogonal factors that were consistent across two sets of menstrual cycle data. These were a negative affect dimension with concomitant behavioral changes, physical symptoms, agitation, and positive arousal. Cluster analysis of factor scores grouped patients into one of five symptom patterns, the most common of which is a general distress cluster, characterized by symptoms across all dimensions. The LLPDD symptom groups identified are remarkably consistent with those of earlier studies using both normative and clinic samples, and consideration of symptom pattern differences in future research may greatly increase our understanding of this disorder.     

Psychological and sexual functioning among outpatient sexual offenders against children: A Minnesota Multiphasic Personality Inventory (MMPI) cluster analytic study

Multivariate clustering procedures were used to identify homogeneous subgroups of outpatient sex offenders against children (n=110)on the basis of the Minnesota Multiphasic Personality Inventory (MMPI). Results indicated a five-subgroup solution. Two within-normal-limits and two clinically elevated profile subgroups replicated subtypes found in previous cluster analytic studies of child sex offenders. The fifth subgroup appeared similar in MMPI profile pattern and elevation to a previously identified subtype of rapists. Discriminant analyses showed that subgroups differed along dimensions of cognitive disturbance and sexual functioning. Furthermore, levels of psychopathology corresponded with levels of sexual pathology. Results are discussed with reference to previous MMPI cluster analytic studies of sex offenders and theories of sexual aggression.Portions of this paper were presented at the meeting of the Midwestern Psychological Association, 1992, Chicago, Illinois.     

An educational program to overcome language and cultural barriers to genetic services

Providing genetic services to families who do not speak English and whose cultures are quite diverse presents a unique challenge to genetic specialists. One approach that is being employed successfully is the use of specially trained genetic assistants to provide outreach, case finding, referral, support, interpretation, advocacy, and follow-up counseling. A basic genetic assistant training program for five bicultural/bilingual Southeast Asian case managers is described. The course syllabus can be used to train health workers who represent a variety of cultures and languages.     

Evaluating treatment effects in single-subject behavioral experiments using quality-control charts

Quality-control charts can be particularly useful in identifying treatment effects and patterns of behaviors in single-subject behavior-analytic experiments that cannot be determined by visual inspection of their graphs. Using an example from the behavior analysis literature the quality-control charts identified the presence of treatment effects across phases as well as the presence of trends within and between phases. The ease of their calculations suggest use of them by behavior analysts whenever the effects of particular interventions are questionable.     

Attitudes toward maternal serum screening in Chinese women with positive results

Maternal serum screening for fetal Down syndrome has been integrated into routine antenatal care in most clinics in Taiwan. We examined the attitudes toward serum screening and the possible implications in women with positive results. From January to July 1995, 276 women were referred to the Genetic Counseling Clinic, Mackay Memorial Hospital for amniocentesis because of positive screening results, and 214 participated in this study. All women opted for amniocentesis after genetic counseling. Over 40% stated that they made decisions independently after being informed of the serum screening. Need for certainty was the most frequently mentioned reason. Two-thirds believed that serum screening could provide a diagnosis. Almost all women would apply for maternal serum screening for future pregnancies. This study demonstrated that Chinese women need more counseling and autonomy regarding maternal serum screening.     

SLEEP DEPRIVATION,ALLERGY SYMPTOMS,AND NEGATIVELY REINFORCED PROBLEM BEHAVIOR

We studied the relation between the presence versus the absence of sleep deprivation or allergy symptoms and the rate and function of problem behavior. Three students whose problem behavior was negatively reinforced by escape from instruction were studied across several weeks using analogue functional analyses. Our results indicated that the extraexperimental events were associated with (a) termination of instruction functioning as a negative reinforcer, (b) increased rates of negatively reinforced problem behavior, or (c) increased rates of problem behavior across all conditions.     

BRIEF EXPERIMENTAL ANALYSIS OF STIMULUS PROMPTS FOR ACCURATE RESPONDING ON ACADEMIC TASKS IN AN OUTPATIENT CLINIC

Brief multielement designs were used to examine the effects of specific instructional strategies on accuracy of academic performance during outpatient evaluations of 4 children with learning disorders. Instructional strategies that improved accuracy on academic tasks were identified for all participants. These results suggest that the application of experimental analysis methodologies to instructional variables may facilitate the identification of stimulus prompts that are associated with enhanced academic performance.     

Multivariate modelling and personality organization: A comparative study of the Defense Mechanism Test and linguistic expressions

The main aim of the study is to establish an empirical connection between perceptual defences as measured by the Defense Mechanism Test (DMT)–a projective percept-genetic method–and manifest linguistic expressions based on word pattern analyses. The subjects were 25 psychiatric patients with the diagnoses neurotic personality organization (NPO), borderline personality organization (BPO) and psychotic personality organization (PPO) in accordance with Kernberg's theory. A set of 130 DMT variables and 40 linguistic variables were analyzed by means of partial least squares (PLS) discriminant analysis separately and then pooled together. The overall hypothesis was that it would be possible to define the personality organization of the patients in terms of an amalgam of perceptual defences and word patterns, and that these two kinds of data would confirm each other. The result of the combined PLS analysis revealed a very good separation between the diagnostic groups as measured by the pooled variable sets. Among other things, it was shown that NPO patients are principally characterized by linguistic variables, whereas BPO and PPO patients are better defined by perceptual defences as measured by the DMT method.