Low Persistence Rates Research Articles

Survival‐variation within and between functional categories of the African multimammate rat

1.By identifying ecological factors specific to functional categories of individuals, it may be possible to understand the mechanisms underlying life‐history evolution and population dynamics. While empirical analyses within the field of population biology have focused on changes in population size, theoretical models assuming differential sensitivities of population growth rate or fitness to demographic parameters have mostly been untested, particularly against data on small mammals.2.Statistical modelling of capture–mark–recapture data on the multimammate rat (Mastomys natalensis) from Tanzania shows that: (i) females survive slightly better than males and subadults survive much better than adults; (ii) temporal variation of survival of all individuals is similarly related to the rainfall of the month; (iii) subadults exhibit a strongly density‐dependent low persistence rate in the population immediately after their first capture; (iv) subadults survival in later months is, however, positively related to density; and (v) adult survival shows negative density‐dependence.3.Both density‐dependent and density‐independent factors simultaneously determine stage‐dependent survival variation of the multimammate rat. Whereas environmental factors in this population seem to affect survival rates of all individuals in a similar manner, density‐dependent relationships are more complex.4.The patterns of survival variation in small mammals may be different from those observed in large mammals.5.Further studies of demography in small mammals should aim at understanding how much of the variability in population growth rate is accounted for by the variability of the demographic rates resulting from limiting (density‐independent) and regulating (density‐dependent) factors, respectively. This study emphasizes the use of robust and accurate statistical methods as well as stage‐ or age‐structured population modelling.

Risk of hepatitis C infection in neonates transfused with blood from donors infected with hepatitis C.

This look-back study was undertaken to identify newborn infants who had been infected with the hepatitis C virus (HCV) as a result of transfusions received before the introduction of routine screening in 1991 and to determine the transmission rates and persistence of transfusion-transmitted HCV infection acquired in the neonatal period. A total of 24 infants, transfused between 1980 and 1991, were identified as having received potentially infected blood from 11 blood donors. Ten of the donors had been administered batches of anti-D in 1977 known to have transmitted HCV genotype 1b infection. HCV RNA was detected in five of these donors when tested in 1994-95; the past donations of five of the donors, who had received anti-D immunoglobulin and had serological evidence of previous HCV infection but who were PCR negative when tested in 1994-95, were considered of lower risk. The source and time of acquisition of HCV infection for the one remaining donor in the study was not determined. Twenty-one (88%) of the 24 children were living at time of lookback. The median age at transfusion was 12 days. The median age at time of testing was 6.3 years. One child, who tested negative, was excluded from further analysis of HCV transmission, due to incomplete transfusion records. Overall, 12 of 20 (60%) children tested were positive for anti-HCV and seven (35%) were HCV RNA positive. Twelve (71%) of the 17 recipients of viraemic blood were ELISA positive and seven (41%) were PCR positive. Resolved HCV infection, as determined by ELISA pos, RIBA pos or indeterminate and PCR negativity, occurred in five of 12 (42%). In many instances there was more than one recipient per HCV infected donation. All of the reported children are clinically asymptomatic. However, the duration of HCV infection is relatively short and there is evidence of a degree of hepatitis in five of the seven children who are HCV RNA positive as judged by mildly elevated transaminase levels. The three who have undergone liver biopsy show mild hepatitis. The lower rates of persistence of HCV infection in this study may be due to the young age at exposure or to the source of infection which for all but one of the children was linked to one HCV genotype from female donors. Sharing of units of blood among multiple infants should be discouraged.

The Role of Perceptions of Prejudice and Discrimination on the Adjustment of Minority Students to College

College participation by minority students declined in the middle 1980s following a period of sustained growth [21]. This trend was particularly evident among African Americans and Hispanics [46] who exhibited both the lowest participation rates as well as the highest propensity to drop out from college. Porter's [45] analyses of the high-school senior class of 1980, for instance, revealed that Hispanic college students were 13 percent more prone to withdraw from college than were white students, whereas African American college students were 22 percent more likely to drop out than their white counterparts over a six-year period. These low persistence rates (even over extended periods of enrollment in college) are particularly troublesome from a policy perspective given the relationship that the attainment of a bachelor's degree has on subsequent occupational and economic attainment [44]. Several reasons have been advanced to account for these trends. Hauser and Anderson [21] explored the extent to which declines in college participation rates could be attributed to changes in college aspirations as well as to changes in high-school completion rates among African Americans. After analyzing college aspiration trends for both minorities and nonminorities over a period of thirty years and taking into account high-school completion rates and indicators of socioeconomic status, Hauser and Anderson could not find support for this hypothesis. Other researchers have speculated that the decline could be attributed to changes in the composition of federal assistance and to patterns of financing higher education exhibited by minority students. Porter [45] noted that declines in minorities' college participation rates correlated with the growth of student loans at the expense of grants. Olivas [41], Mortenson and Wu [31], and Mortenson [30] observed that African American and Hispanic students were less willing to go into debt to finance their college education than were white students. Moreover, Ekstrom [19] helped to establish and test the proposition that students willing to go into debt to finance their education were more likely to enroll and persist in college. An alternative explanation to the role of finances in the persistence process has stressed the influence of academic preparation for college. Tinto [56] argued that overall differences in persistence rates between minorities and nonminorities were primarily due to differences in their academic preparedness rather than differences in their socioeconomic backgrounds. Tinto further contended that these ability differences arise from prior educational experiences at the elementary and secondary educational levels which tend to favor the educational achievement of nonminorities relative to minorities. Some degree of support has been given to this hypothesis. St. John, Kirshstein, and Noell [50], for instance, reported that the effects of ethnicity disappeared once academic preparation for college was taken into account for the high-school class of 1980. The proposition that a lack of adjustment to predominantly white institutions and that perceptions of prejudice (racial climate) may lower the quality of college experiences of minority students has emerged as a competing explanation for the differences in persistence rates between minority and nonminority college students [for example, 1, 18, 23, 24, 28, 34, 35, 36, 53]. Fleming [18], in particular, has argued that adjustment problems with the curriculum, lack of support services, financial problems and the nature of interpersonal relationships with faculty, peers and academic staff are some of the experiences that negatively impact minority students attending predominantly white institutions. Likewise, Tracey and Sedlacek [57, 58, 59] have contended that noncognitive factors (that is, self-concept, an understanding of racism, and the ability to cope with it) play a more critical role in shaping academic performance in college and persistence decisions among minority students than do cognitive factors such as academic ability and study habits. …

Rectal mucosectomy in the treatment of giant rectal villous tumors.

Rectal mucosectomy, a technique adapted from restorative proctocolectomy, has been used to treat large rectal villous tumors. We compared morbidity, tumor control, and functional outcome following rectal mucosectomy with the results of more conventional transanal excision and piecemeal snaring and fulguration in patients with large rectal villous tumors. We retrospectively reviewed the charts of inpatients who had undergone transanal surgery for villous tumors. Between 1983 and 1993, rectal mucosectomy, transanal excision, and snaring and fulguration were performed, respectively, in 12, 26, and 23 patients with large rectal villous tumors. Tumors treated by rectal mucosectomy had a larger mean diameter (8.5 cm) than those treated by transanal excision or snaring and fulguration (4.5 cm and 4.2 cm, respectively; P < 0.0001, analysis of variance). After a mean follow-up of 47 months, incidence of tumor persistence was 17 percent following rectal mucosectomy, 20 percent following transanal excision, and 40 percent following snaring and fulguration (P = 0.04, chi-squared). Tumor recurrence was 8 percent after rectal mucosectomy compared with 36 and 44 percent, respectively, after transanal excision (P = 0.09, chi-squared) and snaring and fulguration (P = 0.04, chi-squared). Clinically significant postoperative bleeding did not occur after rectal mucosectomy; 17 percent of patients had persistent mild incontinence. Rectal mucosectomy for villous tumors, a new application of an established technique, is safe and associated with low rates of tumor persistence and recurrence. Rectal mucosectomy may result in mild incontinence and should be reserved for large or circumferential lesions. For smaller lesions, transanal excision results are more reliable tumor eradication than snaring and fulguration.

Intraoperative Spermatic Venography During Varicocele Surgery in Adolescents

Intraoperative internal spermatic venography performed immediately following varicocele ligation in the adolescent has been touted as reducing varicocele persistence rates. Previously published data corroborate this statement with low persistence rates. Other series in which venography was not performed report a failure rate of 9 to 30%. During a 5-year period a total of 64 varicocele ligations was performed in 62 male adolescents at our institution. Followup postoperatively revealed an overall varicocele persistence rate of 9%. All patients had intraoperative internal spermatic venography on the affected side. Of 64 venograms 16% had shown collateral drainage that, if not ligated, may have resulted in varicocele persistence. These cases accounted for only 1 of the persistent varicoceles. Additionally, venograms had demonstrated filling of the ipsilateral external iliac vein in 8% of the cases. Despite the fact that no attempt was made to ligate these collaterals, none of these patients had a persistent varicocele. After varicocele ligation 30 of 62 patients were followed long enough to evaluate for testicular catch up growth. Of these 30 patients 24 demonstrated an average relative increase in left testicular volume of 17%. These data support routine intraoperative internal spermatic venography while performing varicocele ligation in the adolescent.

The Effects of a Successional Habitat Mosaic On a Small Mammal Community

Small herbivorous mammals living in successional patchy environments may be affected by both patch size variations and successional changes. If patch size affects densities of residents then larger patches should have higher densities compared to smaller patches because larger patches often have greater habitat diversity and lesser chances of stochastic events destroying the population. If patch size affects length of time animals spend on patches (persistence rates) then smaller patches should have lower persistence rates compared to larger patches because smaller patches contain fewer resources. Larger animals may be constrained by body size, as well as population size, to reside only on the larger patches because smaller patches do not contain enough resources. If successional changes affect resident animals that are host specific on colonizing plant species, then the effects may be noticeable immediately following field abandonment because plant species replacement rates are most rapid then. Four small mammal species were included: Sigmodon hispidus, Reithrodontomys megalotis, Microtus ochrogaster, and Peromyscus maniculatus. The field was divided into patches that varied in area by two orders of magnitude with patches of each size treatment placed in each section of the field. Patch size effects on densities and persistence rates of the four mammal species were tested with analyses of variance. Plant species were grouped according to seven life history traits so as to include relative percent cover of most plant species. Multiple linear regression analyses were used to identify which variables (patch size, field sections, and percent relative cover) significantly explained variations in small mammal densities. Effects of patch size on animal densities and persistence rates varied among animal species. The largest species, Sigmodon hispidus, was never found on the smallest patches, but densities of Reithrodontomys magalotis, Microtus ochrogaster, and Peromyscus maniculatus were often highest on the smallest patches. Animal density variations were often significantly explained by patch size using multiple regression analyses (P ≤ .001). However, lack of consistent trends with respect to the other independent variables included in the equations and variable R2 values suggested that other, unmeasured, variables may have influenced the results. Persistence rates of the three species were often highest on the largest patches. Results suggested that animals visited small patches more often than large patches without staying, and used large patches to create territories. Small and medium patches may have been used as archipelagos of preferred habitat interspersed with less desirable habitat. The first stage of old—field succession was completed by the end of the 3rd yr: perennials replaced annuals as the dominant plant species. Neither patch size nor field sections significantly affected percent cover.

Effects of decisional control and work orientation on persistence in preventive health behavior.

Examined persistence in the daily use of fluoride mouthrinse among adolescents as a function of an induced-choice manipulation concerning self-management strategies and freedom to participate in the program. Seventh-grade boys and girls from urban and suburban schools were randomly assigned to a series of either high- or low-choice decisional control manipulations; their daily, home use of fluoride was monitored over a 20-week period. In order to ameliorate the relatively lower persistence rates found previously among suburban (vs. urban) students, all students were given self-management and action instructions as per previous studies. Although suburban students still declined in persistence relative to urban students, female students who received high choice persisted at a higher rate than girls who received low choice. Boys, for the most part, were unaffected by the manipulation. In addition, students' self-reported work orientation was also positively associated with persistence.

Prevalence of isolated antibody to hepatitis B core antigen in an area endemic for hepatitis B virus infection: implications in hepatitis B vaccination programs.

Of 1,801 Chinese subjects, age 1 to 90 years, screened for hepatitis B surface antigen and antibody (HBsAg, anti-HBs) and antibody to hepatitis B core antigen (anti-HBc), 214 (11.9%) had an isolated, positive anti-HBc result; anti-HBc was reproducibly present in the initial sera in only 66% and persisted after an interval of 2 weeks to 3 months in only 73%. There was a strong correlation between the rates of reproducibility and persistence of isolated anti-HBc and the initial anti-HBc titers. Thirty-two subjects with persistent, isolated anti-HBc received four doses of hepatitis B vaccine (5 micrograms, HEVAC B) at 0, 1, 2 and 12 months: 56% developed a primary anti-HBs response in response to hepatitis B vaccine, 16% developed an anamnestic or secondary anti-HBs response, and 28% were undetectable for anti-HBs even after four doses of vaccine. The low rates of reproducibility and persistence of anti-HBc together with the high rate of primary anti-HBs response to hepatitis B vaccine in subjects with isolated anti-HBc raise doubts as to the reliability of anti-HBc (Corzyme, Abbott Laboratories, North Chicago, Ill.) as a single screening test for hepatitis B infection prior to vaccination and suggests that subjects with isolated anti-HBc, in particular those with low anti-HBc titers, be included in vaccination programs.

Qualitative and quantitative microbiological analysis of sputa of 102 patients with cystic fibrosis.

A microbiological analysis of 102 patients suffering from cystic fibrosis was conducted over a 22 month period. 20 microbial species with the following incidence were identified: Pseudomonas aeruginosa: 83.4%; Candida albicans: 29.4%; Staphylococcus aureus: 24.5%; Staphylococcus epidermidis: 11.8%; Haemophilus influenzae: 11.8%; Streptococcus pneumoniae; 6.9%; Pseudomonas maltophilia: 6.8%; Aspergillus fumigatus: 5.9%. Other species were present in less than 5% of the patients. In the majority of specimens with P. aeruginosa, more than one type (up to six) was detectable. These strains were identical in colony appearance, O-serotype and pyocin-type. Quantitative analysis revealed concentrations of colony-forming units of 10(7) to 10(9) for P. aeruginosa, 10(6) to 10(8) for P. maltophilia, 10(4) to 10(7) for S. aureus, 10(4) to 10(6) for S. epidermidis and 10(4) to 10(7) for C. albicans in the majority of specimens. Significant differences were observed in the time periods during which the pathogens persisted in the patients. Maximum persistence was observed for P. aeruginosa. P. maltophilia and A. fumigatus had about similar persistence rates, which were lower than those for P. aeruginosa but above those for S. aureus and H. influenzae. S. epidermidis was eliminated within shorter periods than S. aureus. C. albicans, although the second most frequent microorganism identified, showed a very low persistence rate. The microbiological analysis confirms results from other research centers (high incidence of P. aeruginosa), but reveals significant regional differences as well (Pseudomonas cepacia not detectable, higher incidence of P. maltophilia and C. albicans). This underlines the necessity for detailed qualitative and quantitative microbiological analysis of sputa from cystic fibrosis patients as a prerequisite for rational analysis of etiological, epidemiological and therapeutical aspects of cystic fibrosis.

Men, Women, and the Premed Persistence Gap: A Normative Alternatives Approach

Recent data indicate that, while almost the same proportion of male and female college freshmen enter undergraduate premedical programs, substantially fewer females eventually apply to medical school. College transcripts from a large eastern university were examined to determine whether the lower persistence rate of females is a consequence of a generally lower level of academic performance. The evidence indicates that the differential rate of application is only slightly determined by sex differences in academic performance. Most of the variance is the consequence of a unique pattern of persistence. Females with moderate and low levels of academic performance are substantially less likely than males with similar levels of performance to apply to medical school, but those with a high level of performance are equally likely to apply. Existing and structural barriers approaches in explaining the persistence gap are assessed in terms of logic and evidence. A normative alternatives approach th...

Black Student, White Campus: Structural, Interpersonal, and Psychological Correlates of Success

Over the past twenty years, significant changes have occurred in Black student college attendance patterns in the United States. Whereas in 1964, 60 percent of Black students attended historically Black institutions, by 1973 the proportion had declined to roughly 25 percent. Until 1968, 80 percent of all undergraduate degrees awarded to Blacks were earned at Black colleges or universities.1 In contrast, during 1978-79 an estimated 56 percent of all bachelor's degrees awarded to Black students were conferred by predominantly white schools.2 Far too little research is available about the consequences and implications of this rapid societal change. Research findings suggest that Black students have not fared well on predominantly white college campuses. Relative to white students, they have lower persistence rates, lower academic achievement levels, less likelihood of enrollment in advanced degree