Characterizing neural coding performance for populations of sensory neurons: comparing a weighted spike distance metrics to other analytical methods.

The identity of sensory stimuli is encoded in the spatio-temporal patterns of responses of the encoding neural population. For stimuli to be discriminated reliably, differences in population responses must be accurately decoded by downstream networks. Several methods to compare patterns of responses have been used by neurophysiologists to characterize the accuracy of the sensory responses studied. Among the most widely used analyses, we note methods based on Euclidean distances or on spike metric distances. Methods based on artificial neural networks and machine learning that recognize and/or classify specific input patterns have also gained popularity. Here, we first compare these three strategies using datasets from three different model systems: the moth olfactory system, the electrosensory system of gymnotids, and leaky-integrate-and-fire (LIF) model responses. We show that the input-weighting procedure inherent to artificial neural networks allows the efficient extraction of information relevant to stimulus discrimination. To combine the convenience of methods such as spike metric distances but leverage the advantages of weighting the inputs, we propose a measure based on geometric distances where each dimension is weighted proportionally to how informative it is. We show that the result of this Weighted Euclidian Distance (WED) analysis performs as well or better than the artificial neural network we tested and outperforms the more traditional spike distance metrics. We applied information theoretic analysis to LIF responses and compared their encoding accuracy with the discrimination accuracy quantified through this WED analysis. We show a high degree of correlation between discrimination accuracy and information content, and that our weighting procedure allowed the efficient use of information present to perform the discrimination task. We argue that our proposed measure provides the flexibility and ease of use sought by neurophysiologists while providing a more powerful way to extract relevant information than more traditional methods.

Determinants of non-compliance and attrition in the elderly.

BACKGROUND: This report identifies demographic and health-related baseline factors associated with non-compliance and attrition in elderly subjects participating in a preventive intervention study over a 4-year follow-up period. METHODS: The Cox proportional hazards model and polychotomous logistic regression were used to evaluate time to clinic assessment non-compliance and type of non-participation. RESULTS: Of 1785 subjects, 35.6 percent were non-compliant during follow-up which meant they were eligible to participate at the time they were contacted but would not or could not return for an assessment. Refusals due to a lack of continuing interest or being too busy,and those citing health problems constituted the major subgroups of non-compliers. Death, unable to contact, and ineligible due to disenrollment or moving away accounted for nearly 20 percent. Four-year compliance was achieved by 44.4 percent of the participants. Time to non-compliance was significantly shorter with older age, lower annual income, poorer personal health ranking, and, to a marginal extent, depression. Lower annual income was associated with all reasons for non-participation including disenrollment or moving. Other factors correlated with specific types of nonparticipation. CONCLUSIONS: These results can be useful in designing more effective cohort maintenance strategies. Greater resources may be allocated to subgroups who are less likely to continue.

Quality perceptions of microbiology services. A survey of infectious diseases specialists.

Opinions about the quality of their primary microbiology laboratory were received from more than 500 practicing infectious diseases specialists by a nationally distributed questionnaire. Approximately 92% of the respondents' primary laboratories were hospital-based. These sophisticated users rated the quality of their microbiology laboratories to be generally high, with bacteriology receiving highest scores and parasitology the lowest scores. Fortunately, the serious problems, such as failing to call a critical result and culture mishandled in the laboratory, were experienced rarely. Laboratories directed by pathologists with specialty microbiology training, PHD microbiologists, and infectious diseases specialists were judged to be of highest quality. American Board of Medical Microbiology certification of the laboratory director was related to higher overall quality perceptions. Whereas physician-customer opinions may not directly measure a laboratory's analytic quality, they are an important performance measure on which laboratories can base quality improvement activities in both service and analytical aspects of performance.

Longitudinal effects of preventive services on health behaviors among an elderly cohort.

This study examines the longitudinal (48 months) effects of a preventive services intervention trial with Medicare beneficiaries. The health promotion intervention incorporated a series of workshops and targeted individualized counseling dealing primarily with nutrition and exercise. All subjects completed a health risk appraisal (HRA) questionnaire, which served as a dependent measure. Results show significant, positive changes in intervention subjects in two activity outcomes, aerobic activity and stretching exercises. Although previous research on this cohort found significant positive changes in nutrition behaviors at 12-month follow-up, these differences were not sustained over the three-year follow-up period. The results offer encouragement that continued research on health promotion will eventually produce protocols for select activities that will improve the status of seniors' health.

Identifying depressive symptoms among elderly Medicare HMO enrollees.

Increasing attention has been devoted to the urgent need for identifying depressive symptomatology at the primary care point of contact for older individuals to prevent more serious disease and potential negative behavioral outcomes. Delivering medical care services in a system that is sensitive to the symptoms of depression may lead to greater cost-effectiveness and improved quality of life. This paper examines the correlates of depression in a random sample of 1800 Medicare beneficiaries enrolled in a risk-sharing HMO. Ten percent of the total sample reported a high degree of depressive symptoms, as measured by the CES-D score. The prevalence of depressive symptoms was significantly higher for those who were not married, reported less well-developed social support networks, had low perceived ability to control future health, or had poorer health status. Depressive symptoms were also associated with a greater number of physician office visits and higher ambulatory charges, although no significant relationship was found for inpatient use or total charges. Practical approaches to monitoring depressive symptomatology at the primary care level in an HMO are suggested.

Item non-response to lifestyle assessment in an elderly cohort.

BACKGROUND: Greater attention is being paid to data quality in surveys of older age groups. In this paper patterns of item non-response are examined in a health risk appraisal instrument administered to an elderly cohort participating in a randomized preventive intervention study. METHODS: The association between demographic and health status factors with the number of non-responses out of 174 items was examined at baseline and at the 12-month follow-up on 1791 subjects. RESULTS: Overall, non-response decreased from baseline to 12 months. The pattern was consistent across the seven major components of the questionnaire. Univariate analyses at baseline found that item non-response increased significantly (P < 0.05) with age, being female, being unmarried, lower annual income, less education, and poorer personal health ranking. Polychotomous logistic regression identified age and personal health ranking as statistically significant at both baseline and 12-month follow-up assessments after controlling for all other factors. In addition, education was significant at baseline. CONCLUSIONS: These results help to identify subgroups of elderly participants who contribute to non-random patterns of missing data.

Changes in health behaviors of older adults: the San Diego Medicare Preventive Health Project.

BACKGROUND: This study presents behavioral outcomes at 1-year follow-up from a preventive services intervention trial with Medicare beneficiaries. METHODS: The health promotion package consisted of goal setting and counseling based on a health risk appraisal and a series of eight educational sessions. All subjects completed a health risk appraisal questionnaire immediately prior to the intervention and 1 year later; this served as the dependent measure. RESULTS: Results indicated that there were significant, positive changes in intervention subjects in activity level and selected nutrition behaviors relative to control subjects. The strengths and weaknesses of a broad-based approach to intervention are discussed.

Compliance with a 12-month assessment in an elderly cohort participating in a preventive intervention study: the San Diego Medicare Preventive Health Project.

Non-compliance in long-term cohort studies contributes to bias in the estimation of study parameters and loss of power in hypothesis testing. This paper identifies baseline factors associated with non-compliance in a 12-month health assessment among elderly participants in the San Diego Medicare Preventive Health Project, a randomized preventive intervention study. A non-complier was defined as a study subject contacted by telephone by study personnel to schedule an appointment for the 12-month health assessment but who would not or could not attend. Of the almost 1600 contacted subjects, 14.1% did not participate in the evaluation. Using logistic regression, non-compliance was found to be associated with older age, intervention group assignment, nonsingle family residence, no alcohol use, and, to a lesser extent, depression. No interactions between group assignment and other baseline factors were detected. These results may be useful in designing cohort maintenance strategies where greater resources may be devoted to participants at higher risk of non-compliance and attrition.

Breast and cervical cancer screening in older women: the San Diego Medicare Preventive Health Project.

BACKGROUND. This study presents rates and correlates of cancer screening, including mammography, clinical breast exam, breast self-examination, and Pap tests, in older women. Age was the predictor of main interest. RESULTS. Among a sample of female Medicare beneficiaries ages 65 and older, who were members of a health maintenance organization, there was a significant, inverse relationship between age and mammography adherence, while controlling for health status, physician utilization, education, and income. The proportions of subjects ages 65-74 and 75+ never having had a mammogram were 17 and 32%, respectively, and the proportions having had annual mammograms were 40 and 28%, respectively. Pap test frequency showed a trend toward an inverse relationship with age, controlling for demographic and health-related variables. In the youngest age group (65-69), 52% had annual Pap tests, whereas in the oldest group (80+), only 36% had annual Pap tests. Age did not predict frequency of clinical breast exam, and the relationship of age to breast self-examination was inconclusive. The role of the physician in promoting cancer screening is discussed.

A descriptive analysis of experienced nurses' clinical reasoning during a planning task.

A Think Aloud (TA) method was employed to collect verbal data from seven clinical nurses as they reviewed a written case study and formulated a plan of care. Protocol Analysis (PA) of the verbal data resulted in a visual representation of each subject's plan of care and provided information regarding the clinical data that subjects used to plan care. The results demonstrated that frequently problems and interventions were inextricably linked and considered in unison rather than during separate steps of a planning process. This finding has implications relative to the current practice within both nursing education and nursing service of focusing on problems and interventions separately when planning care.