Multicollinearity may lead to artificial interaction: an example from a cross sectional study of biomarkers

Collinearity is the situation which arises in multiple regression when some or all of the explanatory variables are so highly correlated with one another that it becomes very difficult, if not impossible, to disentangle their influences and obtain a reasonably precise estimate of their effects. Suppressor variable is one of the extreme situations of collinearity that one variable can substantially increase the multiple correlation when combined with a variable that is only modestly correlated with the response variable. In this study, we describe the process by which we disentangled and discovered multicollinearity and its consequences, namely artificial interaction, using the data from cross-sectional quantification of several biomarkers. We showed how the collinearity between one biomarker (blood lead level) and another (urinary trans, trans-muconic acid) and their interaction (blood lead level* urinary trans, trans-muconic acid) can lead to the observed artificial interaction on the third biomarker (urinary 5-aminolevulinic acid).     

Disturbances of affective prosody in patients with schizophrenia; a cross sectional study

The solutions of nine alpha, omega-bis(3-alkyl(aryl)-4,5-dihydro-1H-1,2,4-triazol-5-on-4-yl) alkanes were titrated with tetrabutylammoniumhydroxide (TBAH) in methanol, using potentiometric methods. The half neutralization potentials values were found for all cases. Potentiometric titration curves of compounds in methanol with 0.03 M TBAH are similar to those of weak acids obtained in aqueous media with strong bases. Methanol is found to be a suitable medium for the weakly acidic compounds titrated since they are poorly dissolved in other organic solvents. A comparison among the compounds having the same alkyl chains between the two ring systems has shown that basicity increases and acidity decreases as the size of alkyl chains increases. However, the compound with a substituted phenyl group was found to be the most acidic one among the examined compounds indicating that phenyl group donates ring electrons less effectively to the system. This can be attributed to the stability of the benzene ring.     

Prevalence of serious eye disease and visual impairment in a north London population: population based, cross sectional study

OBJECTIVE: To estimate the magnitude of serious eye disorders and of visual impairment in a defined elderly population of a typical metropolitan area in England, and to assess the frequency they were in touch with, or known to, the eye care services. DESIGN: Cross sectional survey using two stage cluster random sampling. SETTING: General practices in north London. SUBJECTS: Random sample of people aged 65 and older, drawn from a defined population of elderly people registered with 17 general practice groups. MAIN OUTCOME MEASURES: Proportions and population prevalence estimates were determined for visual acuity, assessed with the person's own spectacles (if any), classified into four categories: prevalence of cataract, age related macular degeneration, and refractive error causing visual impairment and of definite primary open angle glaucoma; and status of contact with eye services. RESULTS: 1547 of 1840 (84%) eligible people were examined. The population prevalence of bilateral visual impairment (visual acuity <6/12) was 30%, of which 72% was potentially remediable. 92 of these 448 cases (21%) had visual acuity <6/60 ("blindness") in one or both eyes. Prevalence of cataract causing visual impairment was 30%; 88% of these people were not in touch with the eye services. The prevalence of vision impairing, age related macular degeneration was 8% and of glaucoma (definite cases) was 3%. Three quarters of the people with definite glaucoma were not known to the eye services. CONCLUSIONS: Untreated visual impairment and eye disorders affect a substantial proportion of people aged 65 years and older. These findings should contribute to the setting up of future strategies for preservation of sight and eye health services in general.     

Contribution of parental blood pressures to association between low birth weight and adult high blood pressure: cross sectional study

OBJECTIVE: To examine the possibility that low birth weight is a feature of the inherited predisposition to high blood pressure. DESIGN: Cross sectional study. SETTING: Primary care medical centre in Edinburgh. SUBJECTS: One offspring of 452 families (231 men and 221 women aged 16-26 years) in whom blood pressure, weight, and height were measured in 1986 and whose parents had blood pressure measured in 1979. Birth weights were obtained from case records (270 offspring) or by questionnaires sent to the mothers (182 offspring). MAIN OUTCOME MEASURES: Birth weight and adult systolic blood pressure in offspring in relation to parental blood pressure. RESULTS: If parental blood pressures were not considered, a 1 kg decrease in birth weight was associated with a 2.24 mm Hg increase in systolic blood pressure of offspring (P = 0.06) after correction for current weight and sex. However, parental blood pressures correlated positively with blood pressure of offspring, and higher maternal blood pressure was associated with lower birth weight (-3.03 g/mm Hg, P < 0.01). After correction for parental blood pressures, a 1 kg decrease in birth weight was associated with only a 1.71 mm Hg increase in the systolic blood pressure of the offspring (P = 0.15). CONCLUSIONS: Low birth weight is a feature of the inherited predisposition to hypertension, perhaps because it is associated with higher maternal blood pressure during pregnancy. Parental blood pressure may be an important confounding factor in the relation between low birth weight and subsequent hypertension.     

Ergonomic stressors and upper extremity disorders in vehicle manufacturing: cross sectional exposure-response trends

Cisplatin, cis-diamminedichloroplatinum(II) (CDDP) is one of the most important anticancer agents, initially producing good responses in various tumors. However, resistance to this drug often develops in various tumors, and additional administration decreases its chemotherapeutic efficacy. The precise mechanism of acquisition of resistance to this drug is still uncertain. However in the present study, we established two CDDP-resistant sublines A431/CDDP1 and A431/CDDP2 from human epidermoid carcinoma cell line A431. These resistant sublines were constituted by exposing A431 cells to a gradually increasing dose of CDDP (A431/CDDP1), and by mutagenic induction with mutagen (A431/CDDP2). A431/CDDP1 and A431/CDDP2 have developed 3.1 and 2.7 times more resistance to CDDP than the original A431 cell in terms of IC50. The two CDDP-resistant sublines showed cross-resistance to the CDDP analogue, carboplatin (CBDCA), but not to other chemotherapeutic drugs such as Adriamycin (ADR) and 5-fluorouracil (5-FU). These CDDP-resistant sublines were transplanted into nude mice to demonstrate the resistance to CDDP treatment in vivo. According to the in vitro assay, the mechanism of resistance in A431/CDDP1 and A431/CDDP2 seems to be based on a reduction of intracellular accumulation of CDDP, because their platinum concentration, which is the major component of CDDP, significantly declined. The established CDDP-resistant sublines may be used in further trials to improve the understanding of the mechanisms of resistance to CDDP.     

Doctors and patients don't agree: cross sectional study of patients' and doctors' perceptions and assessments of disability in multiple sclerosis

OBJECTIVES: To compare the judgments of clinicians on which domains of health in the short form questionnaire (SF-36) would be most important to patients with multiple sclerosis with the opinions of patients themselves; to compare assessment of physical disability in multiple sclerosis by a clinician using Kurtzke's expanded disability status scale and a non-clinically qualified assistant using the Office of Population Census and Surveys' (OPCS) disability scale with self assessment of disability and other domains of health related quality of life by patients using the SF-36 and the EuroQol questionnaire; and to compare the scores of patients for each domain of the SF-36 with control data matched for age and sex. DESIGN: Cross sectional study. SETTING: Clinical department of neurology, Edinburgh. SUBJECTS: 42 consecutive patients with multiple sclerosis attending a neurology outpatient clinic for review or a neurology ward for rehabilitation. MAIN OUTCOME MEASURES: Scores on the SF-36; EuroQol; Kurtzke's expanded disability status scale; the OPCS disability scale. RESULTS: Patients and clinicians disagreed on which domains of health status were most important (chi 2 = 21, df = 7, P = 0.003). Patients' assessment of their physical disability using the physical functioning domain of the SF-36 was highly correlated with the clinicians' assessment (r = -0.87, P < 0.001) and the non-clinical assessment (r = -0.90, P < 0.001). However, none of the measures of physical disability correlated with overall health related quality of life measured with EuroQol, Quality of life correlated with vitality, general health, and mental health in the SF-36, each of which patients rated as more important than clinicians and for each of which patients scored lower than the controls. CONCLUSIONS: Patients with multiple sclerosis and possibly those with other chronic diseases are less concerned than their clinicians about physical disability in their illness. Clinical trials in multiple sclerosis should assess the effect of treatment on the other elements of health status that patients consider important, which are also affected by the disease process, are more closely related to overall health related quality of life, and may well be adversely affected by side effects of treatment.     

Evaluation of validity of British anthropometric reference data for assessing nutritional state of elderly people in Edinburgh: cross sectional study

OBJECTIVES: To evaluate the appropriateness of two sets of commonly used anthropometric reference data for nutritional assessment of elderly people. DESIGN: Cross sectional study. SETTING: Two general practices in Edinburgh. SUBJECTS: 200 independently living men and women aged 75 or over randomly recruited from the age and sex register of the practices. MAIN OUTCOME MEASURES: Weight (kg), knee height (cm), demispan (cm), mid-upper arm circumference (cm), triceps skinfold thickness (mm), arm muscle circumference (cm) body mass index (kg/m2), and demiquet (kg/m2) in men and mindex (kg/m) in women. RESULTS: Men and women in Edinburgh were significantly shorter than those in measured for the Nottingham reference data (demispan 0.79 v 0.80 (P < 0.05) for men and 0.72 v 0.73 (P < 0.01) for women). Comparison with data from South Wales showed that men and women from Edinburgh had significantly greater mid-upper arm circumference, triceps skinfold thickness, and arm muscle circumference. No one fell below the 10th centile of the South Wales data (the commonly used out off point for determining malnutrition) for these measures. CONCLUSIONS: Both sets of reference data commonly used in Britain may be inappropriate for nutritional screening of elderly people in Edinburgh. Contemporary reference data appropriate for the whole of Britain need to be developed, and in the longer term biologically or clinically defined criteria for undernutrition should be established.     

Reproductive pattern, perinatal mortality, and sex preference in rural Tamil Nadu, south India: community based, cross sectional study

OBJECTIVES: To study reproductive pattern and perinatal mortality in rural Tamil Nadu, South India. DESIGN: Community based, cross sectional questionnaire study of 30 randomly selected areas served by health subcentres. SETTING: Rural parts of Salem District, Tamil Nadu, South India. SUBJECTS: 1321 women and their offspring delivered in the 6 months before the interview. MAIN OUTCOME MEASURES: Number of pregnancies, pregnancy outcome, spacing of pregnancies, sex of offspring, perinatal and neonatal mortality rates. RESULTS: 41% of the women (535) were primiparous; 7 women (0.5%) were grand multiparous (> 6 births). The women had a mean age of 22 years and a mean of 2.3 pregnancies and 1.8 live children. The sex ratio at birth of the index children was 107 boys per 100 girls. The stillbirth rate was 13.5/1000 births, the neonatal mortality rate was 35.3/1000, and the perinatal mortality rate was 42.0/1000. Girls had an excess neonatal mortality (rate ratio 3.42%; 95% confidence interval 1.68 to 6.98; this was most pronounced among girls born to multiparous women with no living sons (rate ratio 15.48 (2.04 to 177.73) v 1.87 (0.63 to 5.58) in multiparous women with at least one son alive). CONCLUSIONS: In this rural part of Tamil Nadu, women had a controlled reproductive pattern. The excess neonatal mortality among girls constitutes about one third of the perinatal mortality rate. It seems to be linked to a preference for sons and should therefore be addressed through a holistic societal approach rather than through specific healthcare measures.     

Changes in left ventricular structure and function in patients with white coat hypertension: cross sectional survey

OBJECTIVES: To assess the relation between white coat hypertension and alterations of left ventricular structure and function. DESIGN: Cross sectional survey. SETTING: Augsburg, Germany. SUBJECTS: 1677 subjects, aged 25 to 74 years, who participated in an echocardiographic substudy of the monitoring of trends and determinants in cardiovascular disease Augsburg study during 1994-5. OUTCOME MEASURES: Blood pressure measurements and M mode, two dimensional, and Doppler echocardiography. After at least 30 minutes' rest blood pressure was measured three times by a technician, and once by a physician after echocardiography. Subjects were classified as normotensive (technician <140/90 mm Hg, physician <160/95 mm Hg; n=849), white coat hypertensive (technician <140/90 mm Hg, physician >=160/95 mm Hg; n=160), mildly hypertensive (technician >=140/90 mm Hg, physician <160/95 mm Hg; n=129), and sustained hypertensive (taking antihypertensive drugs or blood pressure measured by a technician >=140/90 mm Hg, and physician >=160/95 mm Hg; n=538). RESULTS: White coat hypertension was more common in men than women (10.9% versus 8.2% respectively) and positively related to age and body mass index. After adjustment for these variables, white coat hypertension was associated with an increase in left ventricular mass and an increased prevalence of left ventricular hypertrophy (odds ratio 1.9, 95% confidence interval 1.2 to 3.2; P=0.009) compared with normotensive patients. The increase in left ventricular mass was secondary to significantly increased septal and posterior wall thicknesses whereas end diastolic diameters were similar in both groups with white coat hypertension or normotension. Additionally, the systolic white coat effect (difference between blood pressures recorded by a technician and physician) was associated with increased left ventricular mass and increased prevalence of left ventricular hypertrophy (P<0.05 each). Values for systolic left ventricular function (M mode fractional shortening) were above normal in subjects with white coat hypertension whereas diastolic filling and left atrial size were similar to those in normotension. CONCLUSION: About 10% of the general population show exaggerated inotropic and blood pressure responses when mildly stressed. This is associated with an increased risk of left ventricular hypertrophy.