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Biomedical subjects

John R Crawford

Publications and source records attributed to John R Crawford.

At least 19 recordsLinked to original sources
PubMed2006

A prospective assessment of SRS-24 scores after endoscopic anterior instrumentation for scoliosis.

STUDY DESIGN: Prospective clinical case series. OBJECTIVE: To evaluate the clinical outcome of anterior endoscopic instrumention for scoliosis using the SRS-24 questionnaire and to examine how these scores change over a 2-year follow-up period. SUMMARY OF BACKGROUND DATA: Anterior endoscopic instrumentation correction has several advantages compared with open procedures. However, the clinical results of this technique using a validated outcome measure have rarely been reported in the literature. METHODS: A total of 83 consecutive patients underwent endoscopic anterior instrumentation performed at a single unit. Patients completed the SRS-24 questionnaire before surgery and at 3, 6, 12, and 24 months after surgery. The SRS-24 scores were compared between each of the follow-up intervals. RESULTS: The pain, general self-image, and function from back condition domains improved after surgery (P < 0.05). Activity level significantly improved between 3 and 6 months, and both function domains improved between 6 and 12 months (P < 0.05). None of the domains increased significantly after 1 year. CONCLUSIONS: Endoscopic anterior instrumentation for scoliosis significantly improved pain, self-image, and function. The greatest improvement in function occurred between 6 and 12 months after surgery. The SRS-24 scores at 1 year from surgery may provide a good indicator of patient outcome in the long-term.

Adolescent↗
PubMed2006

Detecting dissociations in single-case studies: Type I errors, statistical power and the classical versus strong distinction.

Dissociations observed in single-case studies play an important role in building and testing theory in neuropsychology; therefore the criteria used to identify their presence should be subjected to empirical scrutiny. Extending work on classical dissociations, Monte Carlo simulation is used to examine the Type I error rate for two methods of detecting strong dissociations. When a Type I error was defined as misclassifying a healthy control, error rates were low for both methods. When Type I errors were defined as misclassifying patients with strictly equivalent deficits on two tasks, error rates for strong dissociations were high for the "conventional" criteria and were very high when cases misclassified as exhibiting either form of dissociation (strong or classical) were combined (maximum = 55.1%). The power to detect strong and classical dissociations was generally low-to-moderate, but was moderate-to-high in most scenarios when power was defined as the ability to detect either form of dissociation. In most scenarios patients with strong dissociations were more likely to be classified as exhibiting classical dissociations. The results question the practical utility of the distinction between strong and classical dissociations regardless of the criteria employed to test for their presence.

Case-Control Studies↗
PubMed2006

Theory of mind following traumatic brain injury: the role of emotion recognition and executive dysfunction.

A number of studies have now documented that traumatic brain injury (TBI) is associated with deficits in the recognition of basic emotions, the capacity to infer mental states of others (theory of mind), as well as executive functioning. However, no study to date has investigated the relationship between these three constructs in the context of TBI. In the current study TBI participants (N=16) were compared with demographically matched healthy controls (N=17). It was found that TBI participants' recognition of basic emotions, as well as their capacity for mental state attribution, was significantly reduced relative to controls. Performance on both of these measures was strongly correlated in the healthy control, but not in the TBI sample. In contrast, in the TBI (but not the control) sample, theory of mind was substantially correlated with performance on phonemic fluency, a measure of executive functioning considered to impose particular demands upon cognitive flexibility and self-regulation. These results are consistent with other evidence indicating that deficits in some aspects of executive functioning may at least partially underlie deficits in social cognition following TBI, and thus help explain the prevalence of social dysfunction in TBI.

Adult↗
PubMed2006

Hip fracture documentation-the impact of shift systems.

The recent reduction in junior doctors' hours has lead to a change in working patterns. The aim of this study was to assess the effect of this change on documentation in orthopaedic surgery. Over a 6-week period, 25 patients were admitted to our unit with hip fractures. During this period, all junior doctors worked on a 'full-shift' working pattern. For comparison a control group was formed comprising of 29 patients admitted with hip fractures over an earlier 6 weeks when all junior doctors worked on a traditional 'on-call' system. The medical records of each patient were assessed for the quality of medical documentation using a published scoring system. The on-call group scored higher for the standard of documentation compared with the shift system group (mean 24.8 versus mean 21.3), p<0.05. The on-call group also had fewer weekdays without any documented entries in the medical records compared to the shift system group (mean 3.2 days versus mean 4.0 days), p<0.05. A change in the working pattern for junior doctors has lead to a reduction in the quality of medical documentation. With more personnel working fewer hours, maintaining a high standard of documentation is essential for the good clinical care of patients.

Aged↗
PubMed2006

Cognitive and psychosocial correlates of alexithymia following traumatic brain injury.

Changes in emotional and social behaviour are considered to be amongst the most common and debilitating consequences of traumatic brain injury (TBI). Little is known of the effects of TBI on alexithymia, which refers to impairment in aspects of understanding emotions. In the current study TBI patients (N=28) were compared with demographically matched healthy controls (N=31) on the Toronto Alexithymia Scale-20 (TAS-20), a measure that taps three distinct characteristics of the alexithymia concept; difficulty in identifying emotions, difficulty in describing emotions and externally oriented thinking. Patients and controls also completed measures of anxiety, depression, quality of life, and measures of fluency to assess executive function. Patients showed greater levels of alexithymia, in terms of difficulty identifying emotions and reduced introspection. Difficulty in identifying emotions was associated with poorer quality of life, even when depression and anxiety were controlled. Difficulty in identifying emotions was also uniquely associated with executive function deficits. Thus, although studies typically focus on aspects of cognitive change following head injury, these results lend support to Becerra et al.'s (Becerra, R., Amos, A., & Jongenelis, S. (2002). Organic alexithymia: a study of acquired emotional blindness. Brain Injury, 16, 633-645.) notion of an 'organic alexithymia', and suggest that more attention should be focused upon assessment of emotional change post-head injury.

Adolescent↗
PubMed2006

Comparing patients' predicted test scores from a regression equation with their obtained scores: a significance test and point estimate of abnormality with accompanying confidence limits.

In contrast to the standard use of regression, in which an individual's score on the dependent variable is unknown, neuropsychologists are often interested in comparing a predicted score with a known obtained score. Existing inferential methods use the standard error for a new case (s-subN+1) to provide confidence limits on a predicted score and hence are tailored to the standard usage. However, s-subN+1 can be used to test whether the discrepancy between a patient's predicted and obtained scores was drawn from the distribution of discrepancies in a control population. This method simultaneously provides a point estimate of the percentage of the control population that would exhibit a larger discrepancy. A method for obtaining confidence limits on this percentage is also developed. These methods can be used with existing regression equations and are particularly useful when the sample used to generate a regression equation is modest in size. Monte Carlo simulations confirm the validity of the methods, and computer programs that implement them are described and made available.

Confidence Intervals↗
PubMed2006

Impairments in theory of mind shortly after traumatic brain injury and at 1-year follow-up.

Most studies into acquired theory of mind (ToM) deficits assessed patients once, long after the onset of brain injury. As a result, the time course of acquired ToM impairments is largely unknown. The present study examined whether ToM impairments following traumatic brain injury (TBI) recover, remain stable, or worsen over time. Because of the alleged association between ToM and social communication, ToM impairments may deteriorate because of changes in patients' social environment following injury. ToM ability and executive functioning were assessed shortly after injury and at 1-year follow-up. Compared with the orthopedic control group, the TBI group was impaired on ToM and executive functioning tasks at both assessments. Furthermore, the ToM impairments in the TBI group remained stable over time.

Adult↗
PubMed2006

The Prospective and Retrospective Memory Questionnaire (PRMQ): latent structure, normative data and discrepancy analysis for proxy-ratings.

OBJECTIVES: To evaluate the proxy-rating version of the Prospective and Retrospective Memory Questionnaire (PRMQ) and provide norms and methods for score interpretation. DESIGN: Cross-sectional and correlational. METHODS: The PRMQ was administered to a large sample drawn from the general adult population (N=570). Confirmatory factor analysis (CFA) was used to test competing models of its latent structure. Various psychometric methods were applied to provide clinicians with tools for score interpretation. RESULTS: The CFA model with optimal fit specified a general memory factor together with additional prospective and retrospective factors. The reliabilities of the PRMQ were acceptable (.83 to .92), and demographic variables did not influence ratings. Tables are presented for conversion of raw scores on the Total scale and Prospective and Retrospective scales to T scores. In addition, tables are provided to allow users to assess the reliability and abnormality of differences between proxy ratings on the Prospective and Retrospective scales. Finally, tables are also provided to compare proxy-ratings with self-ratings (using data from the present sample and self-rating data from a previous study). CONCLUSIONS: The proxy-rating version of the PRMQ provides a useful measure of everyday memory for use in clinical research and practice.

Adult↗
PubMed2006

Objective neuropsychological test performance of professional divers reporting a subjective complaint of "forgetfulness or loss of concentration".

OBJECTIVE: This study attempted to determine whether the higher prevalence of reported "forgetfulness or loss of concentration" among professional divers can be confirmed using objective neuropsychological tests. Secondary aims were to qualify the functional nature of the complaints and to ascertain whether reduced performance was linked to diving history. METHODS: In a case-control study, the neuropsychological test performance of divers complaining of moderate or severe "forgetfulness or loss of concentration" was compared with two age-matched control groups reporting no or slight "forgetfulness or loss of concentration" ("nonforgetful" divers and "nonforgetful" nondivers). The group differences were analyzed using a multivariate analysis of co-variance, followed by canonical discriminant function analysis. Altogether 102 divers with a complaint, 100 nonforgetful divers, and 100 nonforgetful nondivers completed the study. RESULTS: The overall neuropsychological performance differed significantly between the groups [Pillai's trace: F(24,484)=2.04, P=0.003]. Verbal memory (Logical Memory and the California Verbal Learning Test), current intelligence (Wechsler Abbreviated Scale of Intelligence), and sustained attention (rapid visual processing) were poorer among the divers with a complaint than among the nonforgetful divers or the nonforgetful nondivers. The tests of memory, but not those of executive function, differentiated the divers with complaints from the two control groups. Mixed gas bounce diving and surface oxygen decompression diving, but not other techniques, were negatively associated with memory performance. CONCLUSIONS: A cognitive complaint of divers was confirmed using objective tests of neuropsychological performance. Memory, rather than executive function, was affected at the group level, but only to a mild degree. The relationships between diving experience and neuropsychological test performance were small and only seen with diving techniques used in the offshore oil and gas industry.

Adult↗
PubMed2005

Testing for a deficit in single-case studies: effects of departures from normality.

In neuropsychological single-case research inferences concerning a patient's cognitive status are often based on referring the patient's test score to those obtained from a modestly sized control sample. Two methods of testing for a deficit (z and a method proposed by Crawford and Howell [Crawford, J. R. & Howell, D. C. (1998). Comparing an individual's test score against norms derived from small samples. The Clinical Neuropsychologist, 12, 482-486]) both assume the control distribution is normal but this assumption will often be violated in practice. Monte Carlo simulation was employed to study the effects of leptokurtosis and the combination of skew and leptokurtosis on the Type I error rates for these two methods. For Crawford and Howell's method, leptokurtosis produced only a modest inflation of the Type I error rate when the control sample N was small-to-modest in size and error rates were lower than the specified rates at larger N. In contrast, the combination of leptokurtosis and skew produced marked inflation of error rates for small Ns. With a specified error rate of 5%, actual error rates as high as 14.31% and 9.96% were observed for z and Crawford and Howell's method respectively. Potential solutions to the problem of non-normal data are evaluated.

Bias↗
PubMed2005

When is category specific in Alzheimer's disease?

Mixed findings have emerged concerning whether category-specific disorders occur in Alzheimer's disease. Factors that may contribute to these inconsistencies include: ceiling effects/skewed distributions for control data in some studies; differences in the severity of cognitive deficit in patients; and differences in the type of analysis (in particular, if and how controls are used to analyse single case data). We examined picture naming in Alzheimer's patients and matched elderly healthy normal controls in three experiments. These experiments used stimuli that did and did not produce ceiling effects/skewed data in controls. In Experiment 1, we examined for category effects in individual DAT patients using commonly used analyses for single cases (chi2 and z-scores). The different techniques produced quite different outcomes. In Experiment 2a, we used the same techniques on a different group of patients with similar outcomes. Finally, in Experiment 2b, we examined the same patients but (a) used stimuli that did not produce ceiling effects/skewed distributions in healthy controls, and (b) used statistical methods that did not treat the control sample as a population. We found that ceiling effects in controls may markedly inflate the incidence of dissociations in which living things are differentially impaired and seriously underestimate dissociations in the opposite direction. In addition, methods that treat the control sample as a population led to inflation in the overall number of dissociations detected. These findings have implications for the reliability of category effects previously reported both in Alzheimer patients and in other pathologies. In particular, they suggest that the greater proportion of living than nonliving deficits reported in the literature may be an artifact of the methods used.

Aged↗
PubMed2005

A meta-analytic review of verbal fluency deficits in Huntington's disease.

A meta-analysis of 30 studies with 1,511 participants was conducted to estimate and compare the magnitude of deficits on tests of phonemic and semantic fluency for patients with Huntington's disease (HD) relative to healthy control participants. As has been found for patients with focal frontal cortical lesions (but not for patients with focal temporal cortical lesions), symptomatic HD patients were comparably impaired on tests of phonemic and semantic fluency (rs=.71 and .73, respectively). However, in contrast to patients with focal frontal lobe injuries, fluency deficits did not qualify as differential deficits relative to verbal intelligence or psychomotor speed. Therefore, for patients with HD, deficits on tests of phonemic and semantic fluency do not appear to reflect executive dysfunction but a more generalized cognitive impairment.

Adult↗
PubMed2005

Testing for suspected impairments and dissociations in single-case studies in neuropsychology: evaluation of alternatives using monte carlo simulations and revised tests for dissociations.

In neuropsychological single-case studies, a patient is compared with a small control sample. Methods of testing for a deficit on Task X, or a significant difference between Tasks X and Y, either treat the control sample statistics as parameters (using z and zD) or use modified t tests. Monte Carlo simulations demonstrated that if z is used to test for a deficit, the Type I error rate is high for small control samples, whereas control of the error rate is essentially perfect for a modified t test. Simulations on tests for differences revealed that error rates were very high for zD. A new method of testing for a difference (the revised standardized difference test) achieved good control of the error rate, even with very small sample sizes. A computer program that implements this new test (and applies criteria to test for classical and strong dissociations) is made available.

Computer Simulation↗
PubMed2005

Evaluation of criteria for classical dissociations in single-case studies by Monte Carlo simulation.

The conventional criteria for a classical dissociation in single-case studies require that a patient be impaired on one task and within normal limits on another. J. R. Crawford and P. H. Garthwaite (2005) proposed an additional criterion, namely, that the patient's (standardized) difference on the two tasks should differ from the distribution of differences in controls. Monte Carlo simulation was used to evaluate these criteria. When Type I errors were defined as falsely concluding that a control case exhibited a dissociation, error rates were high for the conventional criteria but low for Crawford and Garthwaite's criteria. When Type I error rates were defined as falsely concluding that a patient with equivalent deficits on the two tasks exhibited a dissociation, error rates were very high for the conventional criteria but acceptable for the latter criteria. These latter criteria were robust in the face of nonnormal control data. The power to detect classical dissociations was studied.

Dissociative Disorders↗
PubMed2005

A meta-analytic review of verbal fluency deficits in schizophrenia relative to other neurocognitive deficits.

INTRODUCTION: A prominent view in the neuropsychological literature is that schizophrenia is particularly associated with executive dysfunction, yet in a meta-analytic review it was concluded that, relative to their general level of intellectual functioning, schizophrenics are not disproportionately impaired on a measure of this construct, the Wisconsin Card Sorting Test (WCST). However, verbal fluency tests may be more valid measures of executive functioning as they are more sensitive to the presence of focal frontal lobe injuries. METHOD: A meta-analysis was conducted on 84 studies comparing the performance of schizophrenics and healthy controls on tests of phonemic and semantic fluency, as well as other cognitive measures presumed to impose only minimal demands on executive functioning. RESULTS: Neither phonemic or semantic fluency deficits qualified as differential deficits relative to general intelligence or psychomotor speed. Patients with schizophrenia were significantly more impaired on semantic relative to phonemic fluency. CONCLUSIONS: As for the WCST, deficits on tests of verbal fluency reflect a more generalised intellectual impairment and not particular difficulties with executive control processes. The larger deficit for semantic relative to phonemic fluency suggests that, in addition to general retrieval difficulties, schizophrenia is associated with compromises to the semantic store.

Journal Article↗
PubMed2005

A meta-analytic review of verbal fluency deficits in depression.

A prominent view in the neuropsychological literature is that depression is particularly associated with deficits in executive control processes. A meta-analysis of 42 studies with 2306 participants was therefore conducted to investigate the sensitivity of tests of verbal fluency to the pressure of this disorder, as there is a great deal of evidence that theses measures are valid markers of executive dysfunction. When the methodology adopted by other meta-analytic reviews was employed, semantic fluency deficits were found to be substantially larger than the phonemic fluency deficits. However, when a more rigorous method of meta-analysis was adopted, this indicated that the measure are in fact broadly equivalent in their sensitivity to depression, as has been found for patients with focal frontal lobe lesions. However, in contrast to patients with focal frontal lobe injuries, neither deficit qualified as a differential deficit relative to psychomotor speed. Therefore, for patients with depression, deficits on tests of phonemic and semantic fluency may not reflect executive dysfunction, but a more generalized impairment. Evidence is presented that tests of phonemic and semantic fluency may aid in the differential diagnosis of patients with depression and those in the early stages of dementia of the Alzheimer's type.

Alzheimer Disease↗
PubMed2005

WAIS III UK: an extension of the UK comparability study.

OBJECTIVES: To correct and augment the sample on which a previous study, assessing the applicability of USA WAIS III norms to the UK population, was based. To repeat this study using the modified sample. DESIGN: The WAIS III UK was administered to a supplementary sample, which was used to enhance and correct the original sample, allowing a better match to UK population demographics. METHOD: WAIS III UK scores were processed using USA norms. RESULTS: Distributions of UK IQ, Index, and subtest scores were consistent with USA norms. Means were significantly above USA values and did not show a flat profile. Correlational analysis suggested the presence of an age-related sampling bias, which was then statistically controlled for using analysis of covariance, with age as covariate, to give corrected means. These means, with the exception of two subtests (block design and picture arrangement), did not differ significantly from USA values. CONCLUSION: With a minor proviso concerning the above subtests, it is probable that USA norms can be safely used with the UK population. Future UK samples need to ensure random sampling within demographic categories if sampling bias is to be avoided.

Adolescent↗