A Winnow-Based Approach to Context-Sensitive Spelling Correction

A large class of machine-learning problems in natural language require the characterization of linguistic context. Two characteristic properties of such problems are that their feature space is of very high dimensionality, and their target concepts refer to only a small subset of the features in the space. Under such conditions, multiplicative weight-update algorithms such as Winnow have been shown to have exceptionally good theoretical properties. We present an algorithm combining variants of Winnow and weighted-majority voting, and apply it to a problem in the aforementioned class: context-sensitive spelling correction. This is the task of fixing spelling errors that happen to result in valid words, such as substituting "to" for "too", "casual" for "causal", etc. We evaluate our algorithm, WinSpell, by comparing it against BaySpell, a statistics-based method representing the state of the art for this task. We find: (1) When run with a full (unpruned) set of features, WinSpell achieves accuracies significantly higher than BaySpell was able to achieve in either the pruned or unpruned condition; (2) When compared with other systems in the literature, WinSpell exhibits the highest performance; (3) The primary reason that WinSpell outperforms BaySpell is that WinSpell learns a better linear separator; (4) When run on a test set drawn from a different corpus than the training set was drawn from, WinSpell is better able than BaySpell to adapt, using a strategy we will present that combines supervised learning on the training set with unsupervised learning on the (noisy) test set.Comment: To appear in Machine Learning, Special Issue on Natural Language Learning, 1999. 25 page

Applying Winnow to Context-Sensitive Spelling Correction

Multiplicative weight-updating algorithms such as Winnow have been studied extensively in the COLT literature, but only recently have people started to use them in applications. In this paper, we apply a Winnow-based algorithm to a task in natural language: context-sensitive spelling correction. This is the task of fixing spelling errors that happen to result in valid words, such as substituting {\it to\/} for {\it too}, {\it casual\/} for {\it causal}, and so on. Previous approaches to this problem have been statistics-based; we compare Winnow to one of the more successful such approaches, which uses Bayesian classifiers. We find that: (1)~When the standard (heavily-pruned) set of features is used to describe problem instances, Winnow performs comparably to the Bayesian method; (2)~When the full (unpruned) set of features is used, Winnow is able to exploit the new features and convincingly outperform Bayes; and (3)~When a test set is encountered that is dissimilar to the training set, Winnow is better than Bayes at adapting to the unfamiliar test set, using a strategy we will present for combining learning on the training set with unsupervised learning on the (noisy) test set.Comment: 9 page

Does Openness to Trade Make Countries More Vulnerable to Sudden Stops, or Less? Using Gravity to Establish Causality

Openness to trade is one factor that has been identified as determining whether a country is prone to sudden stops in capital inflows, crashes in currencies, or severe recessions. Some believe that openness raises vulnerability to foreign shocks, while others believe that it makes adjustment to crises less painful. Several authors have offered empirical evidence that having a large tradable sector reduces the contraction necessary to adjust to a given cut-off in funding. This would help explain lower vulnerability to crises in Asia than in Latin America. Such studies may, however, be subject to the problem that trade is endogenous. Using the gravity instrument for trade openness, which is constructed from geographical determinants of bilateral trade, this paper finds that openness indeed makes countries less vulnerable, both to severe sudden stops and currency crashes, and that the relationship is even stronger when correcting for the endogeneity of trade.

The repeatability of self-reported exposure after miscarriage

BACKGROUND: The Avon Longitudinal Study of Pregnancy and Childhood is a prospective study of women who were resident in Avon and who were expected to deliver a baby between April 1991 and December 1992. METHODS: The study provided an opportunity to test the repeatability of responses from 220 women who experienced a miscarriage and who reported exposure to occupational substances and common household products and appliances in two questionnaires. The first questionnaire was completed in the early part of the pregnancy and the second after the miscarriage. Women were asked to score their frequency of exposure on a five-point scale from 'daily' to 'never'. Their responses were analysed to assess the degree of agreement between replies to identical questions in the two questionnaires using the kappa statistic. A new frequency variable was created which compared the replies for the two questionnaires; this was analysed for all exposures by cross-tabulation with possible explanatory variables (age of mother, social class, history of miscarriage and the time lag between questionnaires). RESULTS: In general there was good agreement in the reported exposures to 48 substances and products. The results showed a small and consistent pattern of reporting exposures less frequently in the second questionnaire, i.e. after miscarriage. This was not explained by the analysis of possible confounding variables. Given the literature, the authors had expected to find a shift in the opposite direction. CONCLUSION: The study reinforces the need to be cautious when using the results from single surveys of retrospective self-reported exposure

A Bayesian hybrid method for context-sensitive spelling correction

Two classes of methods have been shown to be useful for resolving lexical ambiguity. The first relies on the presence of particular words within some distance of the ambiguous target word; the second uses the pattern of words and part-of-speech tags around the target word. These methods have complementary coverage: the former captures the lexical ``atmosphere'' (discourse topic, tense, etc.), while the latter captures local syntax. Yarowsky has exploited this complementarity by combining the two methods using decision lists. The idea is to pool the evidence provided by the component methods, and to then solve a target problem by applying the single strongest piece of evidence, whatever type it happens to be. This paper takes Yarowsky's work as a starting point, applying decision lists to the problem of context-sensitive spelling correction. Decision lists are found, by and large, to outperform either component method. However, it is found that further improvements can be obtained by taking into account not just the single strongest piece of evidence, but ALL the available evidence. A new hybrid method, based on Bayesian classifiers, is presented for doing this, and its performance improvements are demonstrated.Comment: 15 page

Assessment worlds colliding? Negotiating between discourses of assessment on an online open course

Using the badged open course, Taking your first steps into Higher Education, this case study examines how assessment on online open courses draws on concepts of assessment used within formal and informal learning. Our experience was that assessment used within open courses, such as massive open online courses, is primarily determined by the requirements of quality assurance processes to award a digital badge or statement of participation as well as what is technologically possible. However, this disregards much recent work in universities that use assessment in support of learning. We suggest that designers of online open courses should pay greater attention to the relationship of assessment and learning to improve participant course completion

Universality in escape from a modulated potential well

We show that the rate of activated escape $W$ from a periodically modulated potential displays scaling behavior versus modulation amplitude $A$. For adiabatic modulation of an optically trapped Brownian particle, measurements yield $\ln W\propto (A_{\rm c} - A)^{\mu}$ with $\mu = 1.5$. The theory gives $\mu=3/2$ in the adiabatic limit and predicts a crossover to $\mu=2$ scaling as $A$ approaches the bifurcation point where the metastable state disappears.Comment: 4 pages, 3 figure

How effective are risk assessments/measures for predicting future aggressive behaviour in adults with intellectual disabilities (ID): A systematic review and meta-analysis

Background: Risk assessments assist professionals in the identification and management of risk of aggression. The present study aimed to systematically review evidence on the efficacy of assessments for managing the risk of physical aggression in adults with intellectual disabilities (ID). Methods: A literature search was conducted using the databases PsycINFO, EMBASE, MEDLINE, Web of Science, and Google Scholar. Electronic and hand searches identified 14 studies that met the inclusion criteria. Standardised mean difference effect sizes Area Under Curve (AUC) were calculated for studies. Random effects subgroup analysis was used to compare different types of risk measures (Actuarial, Structured Professional Judgment and dynamic), and prospective vs. catch-up longitudinal study designs. Results: Overall, evidence of predictive validity was found for risk measures with ID populations: (AUC) = 0.724, 95% CI [0.681, 0.768]. There was no variation in the performance of different types of risk measures, or different study design. Conclusions: Risk assessment measures predict the likelihood of aggression in ID population and are comparable to those in mainstream populations. Further meta-analysis is necessary when risk measures are more established in this population

Holidaying with the family pet: No dogs allowed!

This paper assesses the extent to which dog owners located in Brisbane, Australia, wish to holiday with their pets, and whether there is a gap between this desire and reality. The paper also examines the extent to which this demand is being catered for by the tourism accommodation sector. The need for this study reflects the increasingly significant role dogs are playing in the lives of humans, and the scale of the dog-owning population. The results suggest that, although there is a strong desire among dog owners to take holidays with their pets, the actualisation of this desire is comparatively low. A significant obstacle to the realisation of this desire appears to be a dearth of pet-friendly accommodation. This has implications for the ability of the tourism industry to benefit from this potentially lucrative market, that is, the dog-owning population

Fifty years of spellchecking

A short history of spellchecking from the late 1950s to the present day, describing its development through dictionary lookup, affix stripping, correction, confusion sets, and edit distance to the use of gigantic databases