1. Introduction and Overview. 2. Detecting Influential Observations and Outliers. 3. Detecting and Assessing Collinearity. 4. Applications and Remedies. 5. Research Issues and Directions for Extensions. Bibliography. Author Index. Subject Index.

Regression Diagnostics: Identifying Influential Data and Sources of Collinearity

OBJECTIVES: To establish the prevalence of sarcopenia in older Americans and to test the hypothesis that sarcope- nia is related to functional impairment and physical dis- ability in older persons. DESIGN: Cross-sectional survey. SETTING: Nationally representative cross-sectional sur- vey using data from the Third National Health and Nutri- tion Examination Survey (NHANES III). PARTICIPANTS: Fourteen thousand eight hundred eigh- teen adult NHANES III participants aged 18 and older. MEASUREMENTS: The presence of sarcopenia and the relationship between sarcopenia and functional impairment and disability were examined in 4,504 adults aged 60 and older. Skeletal muscle mass was estimated from bioimped- ance analysis measurements and expressed as skeletal mus- cle mass index (SMIskeletal muscle mass/body mass � 100). Subjects were considered to have a normal SMI if their SMI was greater than -one standard deviation above the sex-specific mean for young adults (aged 18-39). Class I sarcopenia was considered present in subjects whose SMI was within -one to -two standard deviations of young adult values, and class II sarcopenia was present in subjects whose SMI was below -two standard deviations of young adult values. RESULTS: The prevalence of class I and class II sarcope- nia increased from the third to sixth decades but remained relatively constant thereafter. The prevalence of class I (59% vs 45%) and class II (10% vs 7%) sarcopenia was greater in the older ( � 60 years) women than in the older men ( P � .001). The likelihood of functional impairment and disability was approximately two times greater in the older men and three times greater in the older women with class II sarcopenia than in the older men and women with a normal SMI, respectively. Some of the associations be- tween class II sarcopenia and functional impairment re- mained significant after adjustment for age, race, body mass index, health behaviors, and comorbidity. CONCLUSIONS: Reduced relative skeletal muscle mass in older Americans is a common occurrence that is signifi- cantly and independently associated with functional im- pairment and disability, particularly in older women. These observations provide strong support for the prevailing view that sarcopenia may be an important and potentially re- versible cause of morbidity and mortality in older persons. J Am Geriatr Soc 50:889-896, 2002.

Low relative skeletal muscle mass (sarcopenia) in older persons is associated with functional impairment and physical disability.

http://drop-kicker.com/wp-content/uploads/2014/01/kyle-bia.pdf

Bioelectrical impedance analysis--part I: review of principles and methods.

OBJECTIVE: To evaluate whether the homeostasis model assessment (HOMA) is a reliable surrogate measure of in vivo insulin sensitivity in humans. RESEARCH DESIGN AND METHODS: In the present study, we compared insulin sensitivity as assessed by a 4-h euglycemic (approximately 5 mmol/l) hyperinsulinemic (approximately 300 pmol/l) clamp with HOMA in 115 subjects with various degrees of glucose tolerance and insulin sensitivity. RESULTS: We found a strong correlation between clamp-measured total glucose disposal and HOMA-estimated insulin sensitivity (r = -0.820, P

https://care.diabetesjournals.org/content/diacare/23/1/57.full.pdf

Homeostasis model assessment closely mirrors the glucose clamp technique in the assessment of insulin sensitivity: studies in subjects with various degrees of glucose tolerance and insulin sensitivity.

Bioelectrical impedance analysis-part II: utilization in clinical practice.

Assessment of fat-free mass using bioelectrical impedance measurements of the human body

This study was conducted to validate the relationship between bioelectrical conductance (ht2/R) and densitometrically determined fat-free mass, and to compare the prediction errors of body fatness ...

Validation of tetrapolar bioelectrical impedance method to assess human body composition.

Mathematical equations using tetrapolar bioelectrical resistive (R) and reactive (Xc) impedance measures were developed and crossvalidated to predict total body water (TBW) and corrected bromide space (CBS) in two independent samples (n = 110). Height2 per low R was the best predictor of TBW (R = 0.96) and CBS (R = 0.92). When the influence of TBW was removed from CBS and dependent variables, height2 per low Xc was the best predictor (R = 0.50) of CBS. Double crossvalidation of each sample showed that observed and predicted TBW (R = 0.978 and 9.986) and CBS (0.937 and 0.907) were significantly related (p less than 0.001), and there was no difference (p greater than 0.05) between the values. The lines representing the relationships between observed and predicted values had regression coefficients not different than the line of identity. Data from both samples were combined to give a representative multiple regression equation to predict TBW and CBS. This study establishes the validity of the tetrapolar bioelectrical impedance method to assess body fluid volumes in humans.

Estimation of body fluid volumes using tetrapolar bioelectrical impedance measurements.

Signs of copper depletion were produced in a healthy man by an amount of dietary copper (0.83 mg/day) similar to that in some contemporary diets. Urinary and fecal loss of copper exceeded intake. Plasma copper, ceruloplasmin, and superoxide dismutase activity in erythrocytes decreased. Cholesterol in plasma increased, and hematologic indices were unchanged. Lipid metabolism may be a more sensitive index of copper nutriture than are changes in hematology. The findings support the hypothesis that inadequate copper nutriture or altered copper metabolism contributes to the occurrence of ischemic heart disease.

William W. Bolonchuk

Papers

Assessment of fat-free mass using bioelectrical impedance measurements of the human body

Validation of tetrapolar bioelectrical impedance method to assess human body composition.

Estimation of body fluid volumes using tetrapolar bioelectrical impedance measurements.

Increased cholesterol in plasma in a young man during experimental copper depletion.

Chromium supplementation and resistance training: effects on body composition, strength, and trace element status of men