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Timothy T Brown

Publications and source records attributed to Timothy T Brown.

10 recordsLinked to original sources
PubMed2007

How do we measure shortages of dental hygienists and dental assistants? Evidence from California: 1997-2005.

BACKGROUND: The authors examined the labor market for registered dental hygienists (RDHs) and dental assistants (DAs) in California from 1997 to 2005 to determine whether there was a shortage in either market. METHODS: This analysis used economic indicators interpreted within an economic framework to investigate trends in labor force numbers and market-determined wages for RDHs and DAs. Rising inflation-adjusted mean wages indicated a labor shortage, while declining inflation-adjusted mean wages indicated a labor surplus. RESULTS: From 1999 to 2002, the wages for RDHs increased 48 percent and then stabilized, indicating a shortage had occurred, after which the market achieved equilibrium. Wages for DAs increased 13.9 percent from 1997 to 2001, but then declined from 2001 to 2005, indicating a shortage that then became a surplus. The market for DAs may not have stabilized. CONCLUSIONS: Wages increased for RDHs and DAs, suggesting that labor shortages occurred in both markets. The large supply response in the market for DAs resulted in wages declining after their initial rise. PRACTICE IMPLICATIONS: Tracking the local labor markets for RDHs and DAs will enable dental professionals to respond more efficiently to market signals.

California↗
PubMed2006

fMRI reveals novel functional neuroanatomy in a child with perinatal stroke.

Children who have experienced a perinatal stroke often develop normal language function, but the neurobiologic mechanisms underlying this plasticity remain unclear. In this study, we used fMRI to compare, at two ages, the functional neuroanatomy of a child with perinatal stroke with that of age-appropriate cohorts of typically developing children. Although the data for this child are similar to the control group, there are age-dependent differences.

Adolescent↗
PubMed2006

The empirical relationship between community social capital and the demand for cigarettes.

We show that the proportion of community social capital attributable to religious groups is inversely and strongly related to the number of cigarettes that smokers consume. We do not find overall community social capital or the proportion of community social capital attributable to religious groups to be related to the overall prevalence of smoking. Using a new validated measure of community social capital, the Petris Social Capital Index and three years (1998-2000) of US data on 39 369 adults, we estimate a two-part demand model incorporating the following controls: community-level fixed effects, price (including excise taxes), family income, a smuggling indicator, nonsmoking regulations, education, marital status, sex, age, and race/ethnicity.

Adult↗
PubMed2006

Do physicians always flee from HMOs? New results using dynamic panel estimation methods.

OBJECTIVE: To assess the impact of changes in relative health maintenance organization (HMO) penetration on changes in the physician-to-population ratio in California counties when changes in the economic conditions in California counties relative to the U.S. average are taken into account. DATA SOURCES: Data on physicians who practiced in California at any time from 1988 to 1998 were obtained from the AMA Masterfile. The analysis was restricted to active, patient care physicians, excluding medical residents. Data on other covariates in the model were obtained from the Bureau of Economic Analysis, InterStudy, the Area Resource File, and the California state government. Data were merged using county FIPS codes. STUDY DESIGN: Changes in the physician-to-population ratio in California counties include the effects of both intrastate migration and interstate migration. A reduced-form model was estimated using the Arellano-Bond dynamic panel estimator. Economic conditions in California relative to the U.S. were measured as the ratio of county-level real per capita income to national-level real per capita income. Relative HMO penetration in California was measured as the ratio of county-level HMO penetration to HMO penetration in the U.S. relative HMO penetration was instrumented using five identifying variables to address potential endogeneity. Omitted-variable bias was controlled for by first differencing the model. The model also incorporated eight other covariates that may be associated with the demand for physicians: the percentage of the population enrolled in Medicaid, beds in short-term hospitals per 100,000 population, the percentage of the population that is black, the percentage of the population that is Hispanic, the percentage of the population that is Asian, the percentage of the population that is below age 18, the percentage of the population that is aged 65 and older, and the percentage of the population that are new legal immigrants in a given year. All of the above variables were lagged one period. The lagged physician-to-population ratio was also included to control for the supply of physicians. Separate equations were estimated for primary care physicians and specialist physicians. PRINCIPAL FINDINGS: Changes in lagged relative HMO penetration are negatively associated with changes in specialist physicians per 100,000 population. However, this effect of HMO penetration is attenuated and at times reversed in areas where the magnitude of the difference in relative economic conditions is sufficiently large. We did not find any statistically significant effects for primary care physicians. CONCLUSIONS: Consistent with prior studies, we find that changes in physician supply are associated with changes in relative HMO penetration. Relative economic conditions are an important moderator of the effect of changes in relative HMO penetration on physician migration.

California↗
PubMed2006

A comparison of analysis of variance and correlation methods for investigating cognitive development with functional magnetic resonance imaging.

Statistical approaches used in functional magnetic resonance imaging (fMRI) to study cognitive development are varied and evolving. Two approaches have generally been used. These are between-group end-point analysis of variance (ANOVA) and age-related regression. Differences in these 2 approaches could produce different results when applied to a single data set. Event-related fMRI data from a group of typically developing participants (n = 95; age range = 7-35 years) performing controlled lexical processing tasks were analyzed using both methods. Results from the 2 approaches showed significant overlap, but also noteworthy differences. The results suggest that for regions showing age-related changes, correlation was relatively more sensitive to more linear changes whereas ANOVA was relatively more sensitive to less-linear changes. These findings suggest that full characterization of developmental dynamics will require converging methodologies.

Adolescent↗
PubMed2005

Sex and racial/ethnic disparities in outcomes after acute myocardial infarction: a cohort study among members of a large integrated health care delivery system in northern California.

BACKGROUND: Previous studies have documented sex and racial/ethnic disparities in outcomes after acute myocardial infarction (AMI), but the explanation of these disparities remains limited. In a setting that controls for access to medical care, we evaluated whether sex and racial/ethnic disparities in prognosis after AMI persist after consideration of socioeconomic background, personal medical history, and medical management. METHODS: We conducted a prospective cohort study of the members (20,263 men and 10,061 women) of an integrated health care delivery system in northern California who had experienced an AMI between January 1, 1995, and December 31, 2002, and were followed up for a median of 3.5 years (maximum, 8 years). Main outcome measures included AMI recurrence and all-cause mortality. RESULTS: In age-adjusted analyses relative to white men, black men (hazard ratio [HR], 1.44; 95% confidence interval [CI], 1.26-1.65), black women (HR, 1.47; 95% CI, 1.26-1.72), and Asian women (HR, 1.37; 95% CI, 1.13-1.65) were at increased risk of AMI recurrence. However, multivariate adjustment for sociodemographic background, comorbidities, medication use, angiography, and revascularization procedures effectively removed the excess risk of AMI recurrence in these 3 groups. Similarly, the increased age-adjusted risk of all-cause mortality seen in black men (HR, 1.55; 95% CI, 1.37-1.75) and black women (HR, 1.45; 95% CI, 1.27-1.66) was greatly attenuated in black men and reversed in black women after full multivariate adjustment. CONCLUSION: In a population with equal access to medical care, comprehensive consideration of social, personal, and medical factors could explain sex and racial/ethnic disparities in prognosis after AMI.

Adult↗
PubMed2004

Developmental changes in human cerebral functional organization for word generation.

A fundamental issue in cognitive neuroscience is the nature of developmental changes in human cerebral functional organization for higher cognitive functions. Event-related functional magnetic resonance imaging was used to measure developmental changes in the functional neuroanatomy subserving controlled lexical association. First, brain regions showing significant differences in activity between school-age children and young adults, despite equivalent task performance, were identified. Then, activity in these regions was more fully characterized in individuals spanning the ages of 7-32 years old. Cross-sectional and regression analyses showed systematic increases and decreases in levels of activity over age, by region. Age-related increases in activity were primarily newly recruited, later-stage processing regions, such as in left frontal and left parietal cortex. Decreases, on the other hand, were all positive activations that attenuated with age and were found across a wider neuroanatomical range, including earlier processing regions such as bilateral extrastriate cortex. The hemodynamic magnitude, neuroanatomical location and maturational timecourse of these progressive and regressive changes have implications for models of the developing specialization in human cerebral functional organization.

Adolescent↗
PubMed2004

Shared and distinct neurophysiological components of the digits forward and backward tasks as revealed by functional neuroimaging.

The digits forward (DF) and backward (DB) tasks are widely used neuropsychological measures believed to tap overlapping systems of phonological processing and working memory. Studies of focal brain lesions have partially elucidated the brain regions essential for these tasks; however relatively little information exists on the underlying functional neuroanatomy in the intact brain. We therefore examined the shared and separate neural systems of these tasks in two positron emission tomography (PET) experiments. In Experiment 1, eight healthy participants performed verbal DF, DB, and a sensorimotor control task during measurement of regional cerebral blood flow (rCBF). DF and DB each activated frontal, parietal, and cerebellar regions as well as prominently activating medial occipital cortex. To eliminate possible visuospatial confounds, Experiment 2 replicated the first experiment in six additional healthy participants who were blindfolded during the study. No differences in activation were found between the two experimental groups. Combined data from both experiments demonstrate that DF and DB rely upon a largely overlapping functional neural system associated with working memory, most notably right dorsolateral prefrontal cortex (DLPFC) and bilateral inferior parietal lobule (IPL) as well as the anterior cingulate, a region associated with attentional effort. The degree of activation increased linearly with increasing task difficulty in DF. DB additionally recruited bilateral DLPFC, left IPL, and Broca's area. Medial occipital cortex (including higher and lower visual processing areas) was robustly activated in both DF and DB and could not be attributed to visual processing per se, suggesting a possible visual imagery strategy for these aural-verbal tasks.

Adolescent↗
PubMed2002

Functional neuroanatomical differences between adults and school-age children in the processing of single words.

A critical issue in developmental cognitive neuroscience is the extent to which the functional neuroanatomy underlying task performance differs in adults and children. Direct comparisons of brain activation in the left frontal and extrastriate cortex were made in adults and children (aged 7 to 10 years) performing single-word processing tasks with visual presentation; differences were found in circumscribed frontal and extrastriate regions. Conceivably, these differences could be attributable exclusively to performance discrepancies; alternatively, maturational differences in functional neuroanatomy could exist despite similar performance. Some of the brain regions examined showed differences attributable to age independent of performance, suggesting that maturation of the pattern of regional activations for these tasks is incomplete at age 10.

Adolescent↗