In the study described below, the subjects\' body fat was pre-tested and post-te
ID: 3234236 • Letter: I
Question
In the study described below, the subjects' body fat was pre-tested and post-tested to assess the effects of a very-low-calorie diet. Hydrodensitometry measures body fat in water; bioelectrical impedance analysis (BIA) is an electrical measure of body fat.
Seventeen subjects (nine women and eight men) from an outpatient, hospital-based treatment program for obesity volunteered.
Within 10 days after the baseline measures (i.e., pretest measures) were obtained, the subjects began the 12-week VLCD [very low calorie diet] portion of the...program.... At the end of the 12 weeks, all measurements were repeated in the laboratory.
Correlation between hydrostatic weighing and bioelectrical impedance was r = 0.63 for the 16 pretests and r = 0.84 for the 17 posttests. (Hydrostatic measurement of one male subject was not possible on the pretest because of discomfort in the water.) Correlation for the combined pretest and posttest trials (n= 33) was r = .837 (Figure 2 in the next page).
From Figure 2 below, identify the coefficient of X (b) and the intercept (a).
If the line in Figure 2 was extended to the left, at what value would it meet the vertical axis (i.e., y-axis)? (Give an answer that is precise to one decimal place.)
Use the equation for the straight line shown in Figure 2 to predict the percentage of body fat as measured by BIA for a person who has 50% body fat as measured by hydrodensitometry. Make sure the unit of the body fat is “%.”
Use the equation for the straight line shown in Figure 2 to predict the percentage of body fat as measured by BIA for a person who has 20% body fat as measured by hydrodensitometry. Make sure the unit of the body fat is “%.”
50 40 30 Y 5.44 +.77x r .84 20 10 20 40 50 10 Body fat as measured by hydrodensitometry Figure 2. Hydrodensitometry vs. bioelectrical impedance.Explanation / Answer
Answer:
From Figure 2 below, identify the coefficient of X (b) and the intercept (a).
b=0.77
a=5.44
If the line in Figure 2 was extended to the left, at what value would it meet the vertical axis (i.e., y-axis)? (Give an answer that is precise to one decimal place.)
5.4
Use the equation for the straight line shown in Figure 2 to predict the percentage of body fat as measured by BIA for a person who has 50% body fat as measured by hydrodensitometry. Make sure the unit of the body fat is “%.”
predicted the percentage =5.44+0.77*50
=43.94 %
Use the equation for the straight line shown in Figure 2 to predict the percentage of body fat as measured by BIA for a person who has 20% body fat as measured by hydrodensitometry. Make sure the unit of the body fat is “%.”
predicted the percentage =5.44+0.77*20
=20.84
%
Compare your answers to questions #3 and #4. Do your answers make sense considering the coefficient of X (b)? Explain your answer.
Yes, coefficient of X (b) is positive. There is positive relation. When X decreases then y also decreases.