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Search Results: 1 - 10 of 35397 matches for " case-control studies "
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Assessing Likelihood of Having False Positives Caused by Population Stratification  [PDF]
Renfang Jiang, Jianping Dong
Open Journal of Genetics (OJGen) , 2019, DOI: 10.4236/ojgen.2019.91002
Abstract:
Population stratification is always a concern in association analysis. There is a debate on the extent of the problem in less extreme situations (Thomas and Witte [1], Wacholder et al. [2]). Wacholder et al. [3] and Ardlie et al. [4] showed that hidden population structure is not a serious threat to case-control designs. We propose a method of assessing the seriousness of the population stratification before designing association studies. If population stratification is not a serious problem, one may consider using case-control study instead of family-based design to get more power. In a case-control design, we compare chi-square statistics from a structured population (a union of two subpopulations) and a homogeneous population with the same prevalence and allele frequencies. We provide an explicit formula to calculate the chi-square statistics from 17 parameters, such as proportions of subpopulation, allele frequencies in subpopulations, etc. We choose these factors because they have potential to cause false associations. Each parameter takes a random value in a chosen range. We then calculate the likelihood of getting opposite conclusions in the structured and the homogeneous populations. This is the likelihood of having false positives caused by population stratification. The advantage of this method is to provide a cost effective way to choose between using case-control data and using family data before actually collecting those data. We conclude that sample sizes have a significant effect on the likelihood of false positive caused by population stratification. The larger the sample size is, the more likely to have false positive if the population structure is ignored. If the sample size will be smaller than 200 by budget constraints, then case-control study may be a better choice because of its power.
Breastfeeding and breast cancer: a case-control study in Southern Brazil
Tessaro, Sérgio;Béria, Jorge U.;Tomasi, Elaine;Victora, Cesar G.;
Cadernos de Saúde Pública , 2003, DOI: 10.1590/S0102-311X2003000600004
Abstract: to investigate the relationship between breastfeeding and breast cancer in southern brazil, a case-control design was employed, with two age-matched control groups. a total of 250 cases of breast cancer were identified in women from 20 to 60 years of age, with 1,020 hospital and community controls. the main study variables were occurrence of breastfeeding and duration of breastfeeding. a multivariate conditional logistic regression analysis was employed. according to the results, breastfeeding did not have a protective effect against breast cancer. the odds ratio (or) for women who breastfed was 0.9 (95% ci: 0.8-1.2) compared to women who did not breastfeed. for women who breastfed for six months or less, the or was 1.0 (95% ci: 0.6-1.8). in pre-menopausal women who breastfed for more than 25 months, the or was 0.95 (95% ci: 0.5-3.5), and in post-menopausal women or was 1.27 (95% ci: 0.5-3.1), compared to women who had not breastfeed.
Suggestion of an inverse relationship between perception of occupational risks and work-related injuries
Cordeiro, Ricardo;
Cadernos de Saúde Pública , 2002, DOI: 10.1590/S0102-311X2002000100005
Abstract: worker perception of risk influences worker behavior and consequently exposure to risks. however, an inverse relationship between perception of occupational risks and work-related injuries has not yet been clearly established. a matched case-control was performed aiming to investigate possible differences in perception of occupational risks between workers who had suffered occupational injuries and those who had not. cases were defined as all 93 workers from a large metallurgical factory in southeastern brazil, who had suffered occupational injuries during the year 1996. controls were 372 workers who had not suffered occupational injuries, matched on the basis of the factory sector and jobs performed. assessment of occupational risk perception was performed by asking the workers to fill out a questionnaire consisting of questions on specific risks related to problems in work relations, work per se, and mode of production. the findings suggest that the degree of perception that workers with occupational injuries have of some occupational risks is lower than that of their non-injured coworkers.
Fatores associados à idea??o suicida na comunidade: um estudo de caso-controle
Silva, Viviane Franco da;Oliveira, Helenice Bosco de;Botega, Neury José;Marín-León, Letícia;Barros, Marilisa Berti de Azevedo;Dalgalarrondo, Paulo;
Cadernos de Saúde Pública , 2006, DOI: 10.1590/S0102-311X2006000900014
Abstract: this paper aims to identify variables associated with suicidal ideation during the previous 12 months in the city of campinas, s?o paulo, brazil. using a case-control design, risk factors for suicidal ideation were investigated through analysis of independent variables related to the individual, family, and health. some 29 cases of suicidal ideation and 166 controls were interviewed. cases were identified through a previous cross-sectional study, and controls were randomly selected from the same population base among those with no history of suicidal ideation in the previous 12 months. regression models were used to control for confounders and effect modifiers. according to the results, demographic variables were not associated with suicidal ideation. in the final model, the variables that remained statistically significant were depressive symptoms, emotional difficulties, lack of neighborhood support, and less frequent church attendance. suicidal ideation was consistently associated with factors related to depressive symptoms, especially lack of energy and depressed mood.
Fatores dietéticos e cancer oral: estudo caso-controle na Regi?o Metropolitana de S?o Paulo, Brasil
Marchioni, Dirce Maria Lobo;Fisberg, Regina Mara;Góis Filho, José Francisco de;Kowalski, Luiz Paulo;Carvalho, Marcos Brasilino de;Abrah?o, Márcio;Latorre, Maria do Rosario Dias de Oliveira;Eluf Neto, José;Wünsch-Filho, Victor;
Cadernos de Saúde Pública , 2007, DOI: 10.1590/S0102-311X2007000300014
Abstract: dietary factors associated with oral cancer were investigated in a case-control hospital-based study in the city of s?o paulo, brazil, from 1998 to 2002. a total of 835 subjects, 366 with histologically confirmed incident cases of oral-cavity or pharyngeal cancer and 469 controls participated in the study. dietary data were collected with a food frequency questionnaire (ffq). odds ratios (or) and 95% confidence intervals (95%ci) were obtained from unconditional logistic regression, adjusted for potential confounders. inverse associations with risk of oral cancer were found for the highest intake of beans, or = 0.37 (95%ci: 0.22-0.64), raw vegetables, or = 0.51 (95%ci: 0.29-0.93) and the intermediate tertile of rice and pasta intake, or = 0.56 (95%ci: 0.38-0.83). positive associations were observed for the highest intake of eggs, or = 1.84 (95%ci: 1.23-2.75), potatoes, or = 2.22 (95%ci: 1.53-3.25), and milk, or= 1.80 (95%ci: 1.09-2.98). some traditional brazilian foods like rice and beans emerged as protective factors against oral cancer, independently of other risk factors.
Fatores associados ao tracoma em área hipoendêmica da Regi?o Sudeste, Brasil
D'Amaral, Rosa Kazuye Koda;Cardoso, Maria Regina Alves;Medina, Norma Helen;Cunha, Isabel Cristina Kowal Olm;Waldman, Eliseu Alves;
Cadernos de Saúde Pública , 2005, DOI: 10.1590/S0102-311X2005000600017
Abstract: a case-control study matched by age and school (n = 121 pairs) was carried out among pre-elementary and elementary students from low-income families living in greater metropolitan s?o paulo, brazil, with the objective of investigating factors associated with trachoma in a low prevalence area. the case definition for trachoma was that proposed by the world health organization. the dependent variable was trachoma and the independent variables were social stratum, housing of migrants from endemic areas, facial hygiene habits, head of family's schooling, access to potable water, contact with another case in the family, and slum residence. unadjusted and adjusted odds ratios (or), with their respective 95% confidence intervals (95%ci), were estimated by conditional logistic regression. in the multivariate analysis, belonging to the poorest social stratum (or = 8.21; 95%ci: 1.50-44.81), housing people from endemic areas (or = 2.44; 95%ci: 1.10-5.46), contact with another case in the family (or = 2.52; 95%ci: 0.98-6.48), and facial hygiene habits (or = 0.50; 95%ci: 0.26-0.98) were independently associated with trachoma.
Acceso vascular para hemodiálisis con prótesis de politetrafluoroetileno. Reporte de un caso
Otero Reyes,Manuel; Duménigo Arias,Oscar; Gil Hernández,Ailette; Gordis Aguilera,María Victoria;
Revista Archivo M??dico de Camag??ey , 2008,
Abstract: a case of a patient of the nephrology service is presented that is integrated to the hemodialysis program since five years ago by presenting an irreversible chronic renal failure, not able for transplant, with multiple conventional vascular accesses carried out (direct and prosthetic) that have failed by progressive and generalized decay of the vascular system (arterial and venous), due to the effect of the associated pain to the renal disease and the triggering ones by the therapeutic intervention. because of that was surgically intervened and a vascular access at the level of the right inguinal region was performed with the objective to connect the venous system with the arterial one by means of an artificial prosthesis of polytetrafluoroethylene that was implanted in the form of a loop and in superficial planes to facilitate the access to the same one. the use of prosthetic implants of polytetrafluoroethylene in the surgery of vascular access for hemodialysis is a first election alternative when the conventional methods fail.
Susceptibility of asthmatic children to respiratory infection
Pereira,Júlio C. R.; Escuder,Maria Mercedes L.;
Revista de Saúde Pública , 1997, DOI: 10.1590/S0034-89101997000600001
Abstract: objective: a case-control study of patients with pneumonia was conducted to investigate whether wheezing diseases could be a risk factor. methods: a random sample was taken from a general university hospital in s. paulo city between march and august 1994 comprising 51 cases of pneumonia paired by age and sex to 51 non-respiratory controls and 51 healthy controls. data collection was carried out by two senior paediatricians. diagnoses of pneumonia and presence of wheezing disease were independently established by each paediatrician for both cases and controls. pneumonia was radiologically confirmed and repeatability of information on wheezing diseases was measured. logistic regression analysis was used to identify risk factors. results: wheezing diseases, interpreted as proxies of asthma, were found to be an important risk factor for pneumonia with an odds ratio of 7.07 (95%ci= 2.34-21.36), when the effects of bedroom crowding (odds ratio = 1.49 per person, 95%ci= 0.95-2.32) and of low family income (odds ratio = 5.59 against high family income, 95%ci= 1.38-22.63) were controlled. the risk of pneumonia attributable to wheezing diseases is tentatively calculated at 51.42%. conclusion: it is concluded that at practice level asthmatics should deserve proper surveillance for infection and that at public health level pneumonia incidence could be reduced if current world health organisation's guidelines were reviewed as to include comprehensive care for this illness.
Susceptibility of asthmatic children to respiratory infection
Pereira Júlio C. R.,Escuder Maria Mercedes L.
Revista de Saúde Pública , 1997,
Abstract: OBJECTIVE: A case-control study of patients with pneumonia was conducted to investigate whether wheezing diseases could be a risk factor. METHODS: A random sample was taken from a general university hospital in S. Paulo City between March and August 1994 comprising 51 cases of pneumonia paired by age and sex to 51 non-respiratory controls and 51 healthy controls. Data collection was carried out by two senior paediatricians. Diagnoses of pneumonia and presence of wheezing disease were independently established by each paediatrician for both cases and controls. Pneumonia was radiologically confirmed and repeatability of information on wheezing diseases was measured. Logistic regression analysis was used to identify risk factors. RESULTS: Wheezing diseases, interpreted as proxies of asthma, were found to be an important risk factor for pneumonia with an odds ratio of 7.07 (95%CI= 2.34-21.36), when the effects of bedroom crowding (odds ratio = 1.49 per person, 95%CI= 0.95-2.32) and of low family income (odds ratio = 5.59 against high family income, 95%CI= 1.38-22.63) were controlled. The risk of pneumonia attributable to wheezing diseases is tentatively calculated at 51.42%. CONCLUSION: It is concluded that at practice level asthmatics should deserve proper surveillance for infection and that at public health level pneumonia incidence could be reduced if current World Health Organisation's guidelines were reviewed as to include comprehensive care for this illness.
Breastfeeding and breast cancer: a case-control study in Southern Brazil
Tessaro Sérgio,Béria Jorge U.,Tomasi Elaine,Victora Cesar G.
Cadernos de Saúde Pública , 2003,
Abstract: To investigate the relationship between breastfeeding and breast cancer in Southern Brazil, a case-control design was employed, with two age-matched control groups. A total of 250 cases of breast cancer were identified in women from 20 to 60 years of age, with 1,020 hospital and community controls. The main study variables were occurrence of breastfeeding and duration of breastfeeding. A multivariate conditional logistic regression analysis was employed. According to the results, breastfeeding did not have a protective effect against breast cancer. The odds ratio (OR) for women who breastfed was 0.9 (95% CI: 0.8-1.2) compared to women who did not breastfeed. For women who breastfed for six months or less, the OR was 1.0 (95% CI: 0.6-1.8). In pre-menopausal women who breastfed for more than 25 months, the OR was 0.95 (95% CI: 0.5-3.5), and in post-menopausal women OR was 1.27 (95% CI: 0.5-3.1), compared to women who had not breastfeed.
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