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.     

Single-letter recognition accuracy and position information: Benefits with a symbolic cue

Summary This study reports two experiments designed to test a model that has as a basic assumption that position information is at the basis of the cueing benefits observed in single-item recognition tasks with accuracy as the dependent variable. In the experiments, two cueing conditions were used; a 100%-valid symbolic-cue condition and a neutral-cue condition. In Experiment 1, in which position information was sometimes missing, the symbolic cue brought a significant benefit. In Experiment 2, in which position information was always available, no benefit was obtained. These results are consistent with, and support, the model. Improved knowledge of position is at the basis of the cueing benefits observed in this type of task.     

The generation effect in primed word-fragment completion reexamined

Summary Two experiments were designed to test a claim made by Gardiner (1988) that there are generation effects in implicit memory as measured by word-fragment completion. Subjects either read words at study or generated the words from fragments. As in previous research, fragments were completed to a greater extent if they were identical at study and test than if they differed. In Experiment 1 it was found that subjects could recognize explicitly the exact form of fragments that had been used for self-generation and distinguish these from other forms of fragments. An analysis of the contingency relations between recognition of fragments and fragment completion showed a high degree of dependence between the two tests. In Experiment 2 it was found that the match of surface features between study and test was a necessary, but not sufficient, condition to produce enhancement of priming. The results are interpreted as supporting the claim that generation does involve a data-driven component in addition to semantic elaboration.This research was supported by a grant from the Swedish Council for Research in the Humanities and Social Sciences to Lars-Göran Nilsson.     

Daily-life difficulties in person recognition reported by young and elderly subjects

Elderly people frequently complain spontaneously about their inability to remember people and their names. Naturalistic methods such as diaries, checklists, etc. provide useful means to study and make more explicit the nature of such memory difficulties among the elderly, as well as to better understand normal memory functioning. We developed a checklist (inspired by a study by Young, Hay and Ellis, 1985) to explore normal young and elderly people's difficulties in person recognition. The checklist is composed of four parts, each one corresponding to a particular context in which the difficulty took place. Each part has the same structure and consists of precise questions about the type of incident, the circumstances, the persons involved, and the way the incident ended. Three groups of normal subjects kept records of their difficulties and errors in recognizing people for 1 month: young subjects with a bad memory for faces, young subjects without particular problems of face memory, and a group of elderly subjects. A total of 299 records were collected. They were classified with respect to the functional components presumably implied in the process breakdown. The elderly subjects experienced difficulties with retrieving names, first names, or nicknames (Name Codes), while the young subjects with a bad memory for faces reported overall the greatest number of incidents and were particularly impaired in access to Face Recognition Units. A characterization of these two kinds of difficulties is proposed. Young subjects without problems of face memory presented equal numbers of difficulties at all stages of person recognition. These patterns of results will be discussed in terms of current cognitive models of person recognition.     

Acting or listening: Adult age differences in source recall of enacted and nonenacted statements

This study explored age-related differences in item and source recall of enacted and nonenacted items in a sample of healthy adults between the ages of 35 and 80 years (N=1,000). Participants were screened on a variety of demographic, psychometric, and biological variables. They were presented with sentences (e.g., Lift the book) that they either read or enacted. They were then asked to recall the object of each stimulus sentence (item recall) and to identify its format of encoding (source recall). Age-related decrements were observed both in item and source memory, although age differences in source memory were more accentuated than in item memory. Further, the results indicated an overall impairment of source memory across age when individual differences in the demographic, psychometric, and biological variables were taken into consideration.     

Getting ontologically natural

It is argued that Arthur Fine's “natural ontological attitude” (NOA), i.e., the view that science should not be philosophically (either realistically or anti‐realistically) interpreted at all but should rather be allowed to “speak for itself”, is seriously problematic, even though it contains deep insights which philosophers of science should take into account. In particular, Fine succeeds in showing that no non‐question‐begging, conclusive demonstration of scientific realism (e.g., on “explanationist” grounds) is possible. But this is not a threat to scientific realism, if realism is subordinated to pragmatism. From the pragmatic point of view, the demand for a non‐circular proof of scientific realism is mistaken. Rather, realism can be seen as our natural attitude, based on our practices, scientific and otherwise. Fine's NOA turns out to be, on a charitable reading, quite close to a version of pragmatic realism. The paper concludes by briefly examining the idea of regarding realism as a “narrative explanation” of science.     

Interpersonal determinants of attitude change following counterattitudinal behavior

In a test of predictions derived from an identity-analytic model of self-presentational behavior, individuals who privately endorsed positive or negative attitudes about sexual behavior were asked to deliver a prosexuality speech while alone, while watched by observers, or while being watched by observers who questioned the morality of the subject’s actions. Subsequent attitude measures indicated that the subjects who initially adopted negative attitudes justified their behavior by expressing more favorable attitudes about sexuality, but only when no audience witnessed their speech. When an audience was present, these individuals emphasized their lack of choice. In contrast, subjects who privately endorsed positive attitudes publicly expressed less favorable attitudes when their morality was challenged by the observers. These findings suggest that attitude change following counterattitudinal behavior (a) stems from private image-maintenance needs as well as public self-presentational concerns, and (b) is sometimes designed to secure an image of morality as well as an image of consistency.     

Coping with intractable controversies: The case for problem structuring in policy design and analysis

Intractable controversies and other types of policy disagreements correspond to policy problems with a different structure. The more structured a problem is, the more consensus there is about which values and information are at stake in the process of problem solving. Policymakers like to treat problems in as structured a way as possible. Three policy strategies are described to move away from the unstructured to the more structured problem type. However, policymakers run the risk of oversimplifying an ill-structured problem, which means that elements of the problem situation relevant to other actors are overlooked or denied. Hence, policy controversies may become intractable. The remedy is a fourth strategy, characterised by problem structuring. This strategy requires political participation of actors with different views on the problem, and an argued political problem choice. His main research areas are problem structuring in public policy, knowledge use, environmental risk, technology and democracy. He is currently working on knowledge-based policy strategies for addressing the issue of climate change. His research interest is to develop and apply discursive and/or argumentative approaches to the policy process.