Question

You are an analyst working on a Medical Civic Action Program (MEDCAP) mission in the Philippines. The mission is very limited in scope and the primary objective is to provide acute care for recent transplant patients who otherwise would not receive adequate care. Your job is to assess how well the patients’ kidneys are working post-operation (which determines when they can be transferred out of the intensive care unit (ICU) and into rehabilitation). A measure of kidney function is creatinine clearance (measured in ml/minute), essentially measuring how well the kidneys clear creatinine from your system (the higher, the better in these cases). You have also collected data on the patients’ ages (in years) and body mass index (measured as weight(kg)/height(m)2). Interpret the output from your linear regression by answering the following questions:

> fit <- lm(creatinine.clearance~BMI+Age    , data+data)
> summary(fit)
Call:
lm(formla = creatinine.clearance~BMI+Age    , data+data)
Residuals:
Min	1Q	Median	3Q	Max
-152.982	-28.249	-2.378	28.564	198.335
Cofficients
	Estimate	Std Error	t value	Pr(>|t|)
Intercept	74.2744	41.3441	1.796	0.078458	*
BMI	4.2712	1.3614	3.137	0.002857	**
AGE	-1.8798	0.4503	-4.175	0.000119	***
Signif Codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
Residual standard error: 60.49 on 50 degrees of freedom (9 observations deleted due to missingness) Multiple R-squard: 0.375, Adjusted R-squared 0.3375, F-statistic 10 on 3 and 50 DF, p-value: 2.853e-05

A) In your own words, what is the interpretation of the Age coefficient?

B) if you added an independent variable to this analysis, but it had no impact on the creatinine clearance...:

1. R-squared value would increase, thus showing a better fit

2. Adjusted R-squared value would increase, thus showing a better fit

3. Neither adjusted R-squared nor R-squared values would increase

4. R-squared value would increase, but adjusted R-squared would not. Model fit

   using only R-squared values can be misleading.

C) For a 45 year-old with a BMI of 30, what is his expected creatinine clearance?

Show your work.

Answer 1

Solution:-)  

A) The interpretation of the Age coefficient is that creatinine clearance is negatively related with age but as the p-value is smaller than 0.05. Hence, it significantly effect the creatinine clearance.

B) If you added an independent variable to this analysis, but it had no impact on the creatinine clearance, then

R-squared value would increase. Because R-squared variable either remain same or constant but the asjusted R squared decreases by adding variables.

C) For a 45 year-old with a BMI of 30, the expected creatinine clearance will be 117.8239.

CC 74.2744 + 4.2712 BMI 1.8797* Age CC 74.2744 4.2712 30 1.8797 45 117.8239