From book Biostatistics: A foundation for Analysis in the Health Sciences What a
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From book Biostatistics: A foundation for Analysis in the Health Sciences
What are the study questions?
What is the outcome of interest (dependent variable)?
What are the predictors of outcome (independent variables)?
What statistical model was used?
What statistical hypotheses were tested to address the study questions?
What relevant parameters were estimated from the models?
Were the null hypotheses rejected at the level 0.05?
What conclusions should be made based on the statistical analysis results?
Problem 3. For the data described in Exercise 9.3.4, use SAS output provided to address 8 summary questions above. Also, discuss the fit diagnostics in terms of the model assumptions (e.g. do the residuals appear to be normally distributed with a mean of zero and constant variance?)
Reiss et al. (A-3) compared point-of-care and standard hospital laboratory assays for monitoring patients receiving a single anticoagulant or a regimen consisting of a combination of anticoagulants. It is quite common when comparing two measuring techniques, to use regression analysis in which one variable is used to predict another. In the present study, the researchers obtained measures of international normalized ratio (INR) by assay of capillary and venous blood samples collected from 90 subjects taking warfarin. INR, used especially when patients are receiving warfarin, measures the clotting ability of the blood. Point-of-care testing for INR was conducted with the CoaguChek assay product. Hospital testing was done with standard hospital laboratory assays. The authors used the hospital assay INR level to predict the CoaguChek INR level. The measurements are given in the following table.
analysis of variance:
Parameter estimates
source DF sum of squares mean square F value Pr > F model 1 37.85387 37.85387 92.41 <0.0001 error 88 36.05 0.41 corrected total 89 73.90Explanation / Answer
What are the study questions?
ans: The regression model is used to test the significant of 'hospital' (hospital assay INR level) as predictor for dependent variable i.e. CoaguChek INR level. Also, it is building the predictive regression model.
What is the outcome of interest (dependent variable)?
ans: CoaguChek INR level.
What are the predictors of outcome (independent variables)?
ANS: hospital assay INR level
What statistical model was used?
Ans: Simple linear regression model.
What statistical hypotheses were tested to address the study questions?
ans: Following hypothesis are tested:
1) Is regression significant?
2) Is the independent variable a significant predictor?
What relevant parameters were estimated from the models?
ans: model Fit, R-sq, regression intercept and slope
Were the null hypotheses rejected at the level 0.05?
Yes. Both the p-values are less than 5%.
What conclusions should be made based on the statistical analysis results?
Ans: Thre regression model & predictor are significant.
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