Within-subject Differences Research Articles

Parameters of delay discounting assessment: Number of trials, effort, and sequential effects

Procedural variants in estimating delay discounting (DD) have been shown to yield significant within-subject differences in estimated degree of delay discounting as well as variations in the patterns of choice. The purpose of this study was to evaluate the effect of subject control over the number of trials in a delay discounting task, on degree of delay discounting. Participants were assessed with two computerized DD assessments: the full-length method presented participants with a fixed set of 240 trials, and the abbreviated task, where once participants had shown indifference between the immediate and delayed rewards, the remaining trials for that delay value were omitted. While the full-length and abbreviated methods did not differentially affect patterns of choice or estimated delay discounting, the order of presentation (ascending or descending) of immediate rewards produced differences in each measure: rate of delay discounting was significantly lower when estimated with the descending sequence; a larger proportion of area under the discounting curve was concentrated around the indifference point trial with the descending sequence; and a lower correlation was observed between estimates obtained across methods with the descending sequence.

Reliability of quantitative EMG analysis of the extensor carpi radialis muscle

This study investigated the within-subject, intra- and inter-operator reliability of quantitative electromyographic (EMG) analysis using decomposition-based quantitative electromyography (DQEMG). Needle and surface-detected EMG signals were collected during low-level isometric contractions of the extensor carpi radialis (ECR) muscle. DQEMG was used to extract needle-detected motor unit potential (MUP) trains and surface-detected MUPs (SMUPs) associated with each train. Two independent experienced operators re-decomposed and processed the MUP data on two separate occasions. One-way analyses of variance (ANOVA) were performed to identify within-subject differences (test–retest, n = 6), and operator and trial differences (intra- and inter-operator, n = 20) for the MUP morphological variables. The within-subject reliability, as well as the intra- and inter-operator reliability were estimated using intraclass correlation coefficients (ICCs). The 95% limits of agreement were calculated to measure within-subject and between operator agreements. MUP durations were found to be significantly different between days ( p < 0.05). For intra- and inter-operator reliability, a significant difference was found within and between the operators for MUP duration, and between the operators for MUP number of turns ( p < 0.05). SMUP morphological parameters yielded higher ICC values for both intra (0.96–0.99) and inter (0.96–0.99) operator scores when compared to MUP morphological parameters (intra-operator: 0.81–0.99; and inter-operator: 0.67–0.98). Mean motor unit (MU) firing rate was found to be a highly reliable measure for both intra- and inter-operators (0.99–0.97, respectively). The between-operator agreement was above 95% for all morphological parameters. These results concerning within-subject, intra- and inter-operator reliability and levels of agreement for quantitative motor unit analysis suggest that DQEMG provides sufficiently consistent results to allow it to be effectively used for QEMG analysis. Needle-detected MUP morphology although clinically useful in the diagnosis and monitoring of neuropathies, was not as reliable as surface MUP QEMG measures.

Coverage error of three conceptually different shade guide systems to vital unrestored dentition

It remains unclear which shade guide system is most representative of the shades found in the human dentition. The purpose of this study was to determine and to compare the coverage errors (CEs) of 3 different shades in a selected population. The coverage errors of the following shade guide systems were evaluated to determine which shade guide system is most effective in producing the best visual shade match: (1) Vita Lumin, (2) Chromascop, (3) Vitapan 3D Master, and (4) a combination of the 3 shade guide systems. The spectral reflectance values of the central one ninth (1-mm diameter) of each shade tab (without a backing) were measured with a spectroradiometer and an external light source at wavelengths from 380 nm to 780 nm at 2-nm intervals. All spectral reflectance measurements were made using 0-degree observer and 45-degree illumination and then converted to CIE values. The color values of 359 anterior teeth were measured with the same protocol. The CEs for each of the 359 anterior teeth for each shade guide system, and with all 3 shade guide systems, were determined and averaged. Repeated measure ANOVA was used to evaluate the mean minimum CEs within-subject (shade guide system) and between-subject (age) difference as well as the interaction between these variables (alpha=.05). Then, a post hoc multiple comparison was performed using the Tukey-Kramer test. A significant difference (P<.001) was found among the mean minimum CEs of the 3 shade guide systems and their combination, but not between age groups (P=.384). An interaction was found between shade guide systems and age (P<.001). The Tukey-Kramer test revealed that the mean minimum CEs for Vita Lumin (5.39 DeltaE) and Chromoscop (5.28 DeltaE) shade guide systems were not significantly different from each other. However, the combination of all 3 shade guide systems (3.69 DeltaE) and Vitapan 3D Master (3.93 DeltaE) were significantly different from the Vita Lumin and Chromoscop shade guide system. The rankings of the shade guide systems within each age group were similar between the age groups. The Vitapan 3D Master shade guide system resulted in the lowest coverage errors compared to the Vita Lumin or Chromascop shade guide systems. Coverage errors for the Vitapan 3D Master shade guide system did not differ significantly from the coverage errors when all 3 shade guide systems were combined.

Identifying sources of reporting error using measured food intake

To investigate the magnitude and relative contribution of different sources of measurement errors present in the estimation of food intake via the 24-h recall technique. We applied variance decomposition methods to the difference between data obtained from the USDA's Automated Multiple Pass Method (AMPM) 24-h recall technique and measured food intake (MFI) from a 16-week cafeteria-style feeding study. The average and the variance of biases, defined as the difference between AMPM and MFI, were analyzed by macronutrient content, subject and nine categories of foods. Twelve healthy, lean men (age, 39+/-9 year; weight, 79.9+/-8.3 kg; and BMI, 24.1+/-1.4 kg/m2). Mean food intakes for AMPM and MFI were not significantly different (no overall bias), but within-subject differences for energy (EI), protein, fat and carbohydrate intakes were 14, 18, 23 and 15% of daily intake, respectively. Mass (incorrect portion size) and deletion (subject did not report foods eaten) errors were each responsible for about one-third of the total error. Vegetables constituted 8% of EI but represented >25% of the error across macronutrients, whereas grains that contributed 32% of EI contributed only 12% of the error across macronutrients. Although the major sources of reporting error were mass and deletion errors, individual subjects differed widely in the magnitude and types of errors they made.

Identifying sources of reporting error using measured food intake.

To investigate the magnitude and relative contribution of different sources of measurement errors present in the estimation of food intake via the 24-h recall technique. We applied variance decomposition methods to the difference between data obtained from the USDA's Automated Multiple Pass Method (AMPM) 24-h recall technique and measured food intake (MFI) from a 16-week cafeteria-style feeding study. The average and the variance of biases, defined as the difference between AMPM and MFI, were analyzed by macronutrient content, subject and nine categories of foods. Twelve healthy, lean men (age, 39±9 year; weight, 79.9±8.3 kg; and BMI, 24.1±1.4 kg/m2). Mean food intakes for AMPM and MFI were not significantly different (no overall bias), but within-subject differences for energy (EI), protein, fat and carbohydrate intakes were 14, 18, 23 and 15% of daily intake, respectively. Mass (incorrect portion size) and deletion (subject did not report foods eaten) errors were each responsible for about one-third of the total error. Vegetables constituted 8% of EI but represented >25% of the error across macronutrients, whereas grains that contributed 32% of EI contributed only 12% of the error across macronutrients. Although the major sources of reporting error were mass and deletion errors, individual subjects differed widely in the magnitude and types of errors they made.

Functional parameters of delay discounting assessment tasks: Order of presentation

Several variants in the methods used to estimate delay discounting (DD) have been associated with within-subject differences in degree of DD. This study compared variants in the order of presentation of reward and delay values during assessment of DD of hypothetical cash. Participants were randomly assigned to one of two groups. For one group, the immediate reward values were presented in Ascending order and for the other, they were presented in Descending order. In addition, all participants completed a DD task with the reward values presented in a Random order. Degree of DD, calculated as area under the curve (AUC), was similar between the Ascending and Descending procedures, and was significantly higher with the Random procedure. Within-subjects AUC were positively correlated. Reaction times within choice trials changed systematically as a function of order of presentation of the immediate rewards, and distance to the indifference point within each delay value. Reaction times appear to parallel the effort involved in making the individual choices. Some procedural variants in the assessment of DD yield differences in behavior during the assessment task that affect the magnitude of the estimated delay discounting. Thus, the absolute magnitude of DD may not be directly comparable between methods.

A Functional Polymorphism of the μ‐Opioid Receptor Gene (OPRM1) Influences Cue‐Induced Craving for Alcohol in Male Heavy Drinkers

The mu-opioid receptor gene (OPRM1) codes for the mu-opioid receptor, which binds beta-endorphin. The A118G polymorphism in this gene affects beta-endorphin binding such that the Asp40 variant (G allele) binds beta-endorphin 3 times more tightly than the more common Asn40 variant (A allele). This study investigated the influence of the A118G polymorphism on cue reactivity after exposure to an alcoholic beverage in male heavy drinkers. Participants were either homozygous for the A allele (n=84) or carrying at least 1 copy of the G allele (n=24). All participants took part in a cue-reactivity paradigm where they were exposed to water and beer in 3-minute trials. The dependent variables of main interest were subjective craving for alcohol, subjective arousal, and saliva production. G allele carriers reported significantly more craving for alcohol than the A allele participants (as indicated by the within-subject difference in craving after beer vs after water exposure). No differences were found for subjective arousal and saliva. Both groups did not differ in family history of alcoholism. Participants with the G allele reported a significantly higher lifetime prevalence of drug use than participants homozygous for the A allele. A stronger urge to drink alcohol after exposure to an alcoholic beverage might contribute to a heightened risk for developing alcohol-related problems in individuals with a copy of the G allele. The G allele might also predispose to drug use in general.

Variability of Real-World Hearing Protector Attenuation Measurements

The attenuation provided by a hearing protection device (HPD) in the field is usually estimated by applying a derating factor to the laboratory-determined noise reduction rating (NRR) of the HPD. However, attenuation is highly dependent on individual-specific HPD fit. Prediction of an individual's attenuation depends on the accuracy of the measurement system and the variability of attenuation over time (e.g. after HPD refitting). Variability in attenuation and attenuation test systems has not been adequately characterized to allow for such an assessment. This study compared attenuation measurements made with two systems, Real-Ear-at-Threshold (REAT) and Microphone-in-Real-Ear (MIRE), on 20 workers using two earplugs (foam and custom-molded). Workers' perceptions of the earplugs were also evaluated. Individuals' attenuation results were summarized as personal attenuation ratings (PARs, similar to NRRs). Variability in PARs from between-subject, within-subject and within-day (i.e. repeated tests on a subject without earplug refitting) differences was assessed and used to present the lower confidence limit, or uncertainty factor (UF), of an average individual's attenuation. The custom-molded earplug PARs achieved a higher mean percentage of labeled attenuation than did the foam earplug with both test systems. The custom-molded earplugs also had higher overall acceptance among workers. MIRE PAR levels were lower than REAT levels for both earplugs, but the relationship between the two test systems was highly variable. The MIRE system had lower within-day variability than the REAT system. One individual's MIRE results were highly influential; removal of these results greatly reduced the UF for the custom-molded earplug/MIRE combination. UFs ranged from 8.8 to 13.5 dB. These findings highlight the importance of evaluating variability in individual-specific protection results for personal protective equipment like HPDs, rather than relying on single measurements.

Comparative Proteomic Analysis of Intra- and Interindividual Variation in Human Cerebrospinal Fluid

Cerebrospinal fluid (CSF) is a potential source of biomarkers for many disorders of the central nervous system, including Alzheimer disease (AD). Prior to comparing CSF samples between individuals to identify patterns of disease-associated proteins, it is important to examine variation within individuals over a short period of time so that one can better interpret potential changes in CSF between individuals as well as changes within a given individual over a longer time span. In this study, we analyzed 12 CSF samples, composed of pairs of samples from six individuals, obtained 2 weeks apart. Multiaffinity depletion, two-dimensional DIGE, and tandem mass spectrometry were used. A number of proteins whose abundance varied between the two time points was identified for each individual. Some of these proteins were commonly identified in multiple individuals. More importantly, despite the intraindividual variations, hierarchical clustering and multidimensional scaling analysis of the proteomic profiles revealed that two CSF samples from the same individual cluster the closest together and that the between-subject variability is much larger than the within-subject variability. Among the six subjects, comparison between the four cognitively normal and the two very mildly demented subjects also yielded some proteins that have been identified in previous AD biomarker studies. These results validate our method of identifying differences in proteomic profiles of CSF samples and have important implications for the design of CSF biomarker studies for AD and other central nervous system disorders.

Letter Regarding Article by Sega et al, “Prognostic Value of Ambulatory and Home Blood Pressures Compared With Office Blood Pressure in the General Population”

To the Editor: We read with interest the paper by Sega et al regarding the prognostic value of ambulatory, home, and office blood pressure in the PAMELA population.1 However, we find that the main conclusions of the report may be driven by the lack of adjustment for confounders. The relationships between level of blood pressure and risk were not adjusted for age, which may have a major influence on risk over a long time span. There is indeed a relation between age and blood pressure,2 and therefore, these results may be biased. The comparisons of the various blood pressures were also not adjusted for potential confounders, with the argument that “no adjustment for age, sex, and other cardiovascular risk factors was made because comparisons between the predictive value of various blood pressure values involved the same sample.” However, it has been shown in a general Belgian population that the within-subject differences between office and ambulatory blood pressure measurements increased with older age and greater body mass index.3 In addition, in the Danish MONICA population, the within-subject differences between office and ambulatory blood pressure measurements increased with older age, diagnosis of hypertension, male gender, and presence of diabetes.4 So, to assess the true prognostic value of office blood pressure versus that of ambulatory blood pressure, it is mandatory to explore whether adjustments for other relevant cardiovascular risk factors would change the results. Recently, it was shown in the Danish MONICA population that ambulatory blood pressure was a much better predictor of all-cause mortality and cardiovascular mortality than office blood pressure, taking other relevant risk factors into account.5 Accordingly, to make the results from previous studies comparable to the PAMELA study, we would like to know the results of adjusted analyses. Until that time, the conclusion that …

Whole-head MEG analysis of cortical spatial organization from unilateral stimulation of median nerve in both hands: No complete hemispheric homology

We examined the contralateral hemispheric cortical activity in MEG (151 ch) after unilateral median nerve stimulation of the right and left hand in twenty healthy right-handed subjects. The goal was to establish parameters to describe cortical activity of the hemispheric responses and to study the potential ability to assess differences in volunteers and patients. We focused on the within-subject similarity and differences between evoked fields in both hands. Cortical activity was characterized by the overlay display of waveforms (CWP), number of peak stages, loci of focal maxima and minima in each stage, 3D topographic maps and exemplified equivalent current dipole characteristics. The paired-wise test was used to analyze the hemispheric differences. The waveform morphology was unique across the subjects, similar CWPs were noted in both hemispheres of the individual. The contralateral hemispheric responses showed a well defined temporal–spatial activation of six to seven stages in the 500 ms window. Consistently (in over 80% of subjects), the six stages across the subjects were 20M, 30M, 50M, 70M, 90M, and 150M. A 240M was present in the left hemisphere (LH) in 15/20 subjects and in the right hemisphere (RH) in 10/20. Statistics of the latencies and amplitudes of these seven stages were calculated. Our results indicated that the latency was highly consistent and exhibited no statistical mean difference for all stages. Furthermore, no mean amplitude differences between both hemispheres at each stage were found. The patterns of magnetic fields in both hemispheres were consistent in 70% of the subjects. A laterality index (L.I.) was used for defining the magnetic field amplitude differences between two hemispheres for each individual. Overall, the absolute amplitude of the brain responses was larger in the left than in the right hemisphere in the majority of subjects (16/20), yet a significant portion (4/20) exhibited right dominance of the N20m activity. Each individual exhibited a unique CWP, there was reliable consistency of peak latencies and mean amplitudes in median nerve MEG. Nevertheless, this study indicates the limitations of using the intact hemisphere responses to compare with those from the affected (brain) side and suggests caution in assuming full homology in the cortical organization of both hemispheres. This study provides some results to address clinical issues like which parameter describes individual differences best. Whether a genuine difference is found or whether any difference may simply represent the variability encountered in a normal population.

Understanding supervisor-targeted aggression: A within-person, between-jobs design.

The authors investigated predictors of supervisor-targeted workplace aggression among 105 "moonlighters" (employed adults who work 2 jobs, each with a different supervisor), as a way of examining the relative role played by within-subject situational differences and between-subjects individual differences. Individual difference variables (self-esteem, history of aggression) explained a similar level of variance in aggression across both jobs, whereas situational factors (interactional injustice, abusive supervision) were job specific and explained proportionally more variance than did individual differences.

Anti–tumor necrosis factor α blockade in the treatment of juvenile spondylarthropathy

Persistent inflammation refractory to standard antirheumatic therapy in children with juvenile spondylarthropathy (SpA) leads to morbidity and reduced quality of life. Tumor necrosis factor alpha (TNFalpha) plays an important role in the pathogenesis of synovitis and enthesitis. This study was undertaken to examine the impact of anti-TNFalpha agents on juvenile SpA that is refractory to nonsteroidal antiinflammatory drugs (NSAIDs), disease-modifying antirheumatic drugs, and corticosteroids. Ten juvenile SpA patients with a mean +/- SEM age of 15.0 +/- 0.7 years and disease duration of 4.4 +/- 0.8 years, all of whom were HLA-B27 positive, were followed up for 1 year after initiation of either infliximab (n = 8) or etanercept (n = 2). Outcomes examined were within-subject differences in the tender entheseal count (TEC) and active joint count (AJC), markers of inflammation, functional assessments (Childhood Health Assessment Questionnaire [C-HAQ] score), and requirements for antirheumatic drugs. At baseline, all patients exhibited active arthritis and enthesitis that were resistant to NSAIDs (n = 10), methotrexate (n = 6), sulfasalazine (n = 8), corticosteroids (oral n = 6, intravenous pulse n = 3, and intraarticular n = 6), and bisphosphonates (n = 2). In 2 patients, sulfasalazine (n = 2), corticosteroids (n = 1), and bisphosphonates (n = 1) were stopped after initiation of the anti-TNFalpha agent. In all patients, the arthritis and enthesitis significantly improved as evidenced by remission of the TEC and AJC by 6 months that was sustained during the 1-year followup, markers of inflammation and C-HAQ scores normalized, and there was a reduction in requirements for antirheumatic drugs (reduced dosage or discontinuation of NSAIDs n = 10, methotrexate n = 5, sulfasalazine n = 6, corticosteroids n = 4, and bisphosphonates n = 1). Anti-TNFalpha therapy is a potential novel treatment for refractory juvenile SpA. Further prospective studies are required to examine the effectiveness and long-term outcomes of anti-TNFalpha therapy in this cohort.

Lamina-Specific Reductions in Dendritic Spine Density in the Prefrontal Cortex of Subjects With Schizophrenia

In a previous study the authors found that dendritic spine density was reduced on prefrontal pyramidal neurons in layer 3 of subjects with schizophrenia. From a neural circuitry perspective, understanding the pathophysiological significance of this finding requires knowledge of whether pyramidal neurons in other cortical layers are similarly affected. The authors' goal was to determine whether their finding in layer 3 was also present in other cortical layers in the same group of subjects with schizophrenia. Spine density and other dendritic measures were made for pyramidal neurons in layers 5 and 6 of prefrontal area 46 in the brains of deceased subjects with schizophrenia, subjects with other psychiatric disorders, and normal comparison subjects. None of the dendritic measures for layer 5 or 6 pyramidal neurons differed across the subject groups, but the within-subject differences in spine density between deep layer 3 and layer 5 or 6 pyramidal neurons were significantly greater in the patients with schizophrenia than in the comparison subjects. These findings are consistent with the idea that prefrontal pyramidal neurons involved in corticocortical and/or thalamocortical connections are preferentially affected in schizophrenia.

Measuring energy expenditure using heart rate to assess the effects of wheelchair tyre pressure

To investigate the effects of wheelchair tyre pressure on mechanics and energy and explore the use of heart rate as a measurement of energy expenditure. A single factor repeated measures design was used. Four tyre pressures (100, 75, 50, 25 psi) represented a change of workload. Each subject wheeled at a constant self-selected wheeling velocity for 8 min. A total of four trials were completed with a 10-min rest between trials. Oxygen consumption, heart rate and distance travelled were collected during each trial. Three women and 11 men with spinal cord injury. The mean age for the whole group was 34.5 years. The range of lesion level was T4-L1. There was a significant increase is energy expenditure when tyres were deflated to 50 psi from 100 psi. The mean correlation between heart rate and oxygen consumption was 0.74 for all subjects. For the subjects with lesions above T6 and T6 and below the correlations were 0.55 and 0.82, respectively. Tyre pressures below 50% inflation add an additional 25% increase in energy expenditure during wheeling. This could be detected using oxygen consumption or heart rate, as heart rate was shown to have a good correlation with oxygen consumption in the spinal cord injured with lesions below T5. Heart rate does have its limitations and it should only be used to measure within-subject differences.

Comparisons between rumination and worry in a non-clinical population

Major depression is characterised by ruminative thinking whilst worry is considered central in generalised anxiety disorder (GAD). However, not only do these two forms of repetitive negative thinking regularly co-occur in the same individual but similarities between worry and rumination are apparent. Adapting a methodology developed by Langlois et al. (Behav. Res. Therapy 38 (2000) 157–173), this study directly compared worry and rumination in a non-clinical population across a series of variables drawn from current models (appraisal, general descriptors and emotional reactions). Each of 149 female volunteers, with a wide range of age and backgrounds, identified a ruminative thought and a different worry and subsequently evaluated them using the Cognitive Intrusion Questionnaire. Significant within-subject differences were revealed on seven variables: chronicity, unpleasantness, reality of problem, future orientation, past orientation, feelings of worry and insecurity. There were no differences found between worry and rumination on appraisals and strategies, consistent with accounts that propose that worry and rumination share the same processes but involve different content (Cognitive Ther. Res. 24 (2000) 671–688).

Discrimination of Speech Sound Contrasts Determined with Behavioral Tests and Event-Related Potentials in Cochlear Implant Recipients

Cortical potentials evoked with speech stimuli were investigated in ten experienced cochlear implant (CI, type Nucleus 24M) users using three different speech-coding strategies and two different speech contrasts, one vowel (/i/-/a/) and one consonant (/ba/-/da/) contrast. On average, results showed that, compared to subjects with normal hearing, P300 amplitudes were smaller; however, most latencies were within the normal range. Next, individual P300 measures in response to the two speech contrasts were compared to behavioral discrimination scores. Significant within-subject differences in P300 amplitudes and latencies were found for the three speech coding strategies. These differences were in agreement with the behavioral, strategy-dependent discrimination of the speech contrasts.

Reproducibility of intra-arterial ambulatory blood pressure: effects of physical activity and posture.

To examine the effects of physical activity, body posture and sleep quality on the reproducibility of continuous ambulatory blood pressure monitoring. Measurements were performed in 35 subjects (18 hypertensive, 11 male), mean +/- standard deviation age 49 +/- 13 years. Blood pressure (BP) was measured in the brachial artery, and beat-to-beat values of systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure and heart rate (HR) were computed. Physical activity and posture were continuously measured with five accelerometers. Subjective quality of sleep was assessed with a questionnaire. Reproducibility was expressed as an intraclass correlation coefficient and as the standard deviation of the within-subject differences. Posture and activity significantly influenced BP and HR. From lying to sitting, the SBP, DBP and HR increased 6 mmHg, 8 mmHg and 8 beats/min, respectively. From sitting to standing these respective increases were 4 mmHg, 2 mmHg and 13 beats/min. A further rise in activity (from standing to moving generally or walking) increased the SBP by 7 mmHg and the HR by 7 beats/min, and decreased the DBP by 8 mmHg. For daytime SBP, DBP and HR, the intraclass correlation coefficient (standard deviation of the within-subject differences) values were 0.93 (7.2 mmHg), 0.94 (3.8 mmHg) and 0.90 (4.1 beats/min). For night-time these respective values were 0.98 (4.4 mmHg), 0.97 (2.5 mmHg) and 0.96 (2.2 beats/min). Correction for physical activity level and posture hardly improved the reproducibility of daytime BP and HR. Reproducibility of night-time BP and HR was not improved by correction for physical activity, supine position or self-reported sleep quality. Within-subject differences between ambulatory BP recordings cannot be explained by differences in physical activity and body posture.

Generalization between receptive and expressive language in young children with autism

AbstractGeneralization between expressive and receptive language was studied in six boys with autism (chronological age 47–76 months, language age 13–42 months). Each participant received training on three or four word pairs (e.g. hot/cold). Half the pairs were taught expressively and then receptively; the other half were taught in the reverse order. Data were obtained on generalization from the trained to untrained modality, generalization errors, and between‐ and within‐subject differences. Across participants, the ‘expressive first’ condition led to cross‐modal generalization more often than the ‘receptive first’ condition. However, one child displayed the opposite pattern, and three other children's patterns varied across training stimuli. Error analyses indicated that, when children failed to demonstrate receptive‐to‐expressive generalization, they did generalize in another manner: responding based on physical resemblance between cues used in the study and those used in previous training. The results suggest ways to individualize instruction and better understand cross‐modal generalization. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Temporal relation between the ADC and DC potential responses to transient focal ischemia in the rat: a Markov chain Monte Carlo simulation analysis.

Markov chain Monte Carlo simulation was used in a reanalysis of the longitudinal data obtained by Harris et al. (J Cereb Blood Flow Metab 20:28-36) in a study of the direct current (DC) potential and apparent diffusion coefficient (ADC) responses to focal ischemia. The main purpose was to provide a formal analysis of the temporal relationship between the ADC and DC responses, to explore the possible involvement of a common latent (driving) process. A Bayesian nonlinear hierarchical random coefficients model was adopted. DC and ADC transition parameter posterior probability distributions were generated using three parallel Markov chains created using the Metropolis algorithm. Particular attention was paid to the within-subject differences between the DC and ADC time course characteristics. The results show that the DC response is biphasic, whereas the ADC exhibits monophasic behavior, and that the two DC components are each distinguishable from the ADC response in their time dependencies. The DC and ADC changes are not, therefore, driven by a common latent process. This work demonstrates a general analytical approach to the multivariate, longitudinal data-processing problem that commonly arises in stroke and other biomedical research.