Using Control Variables Examining the Relationship Between Nutritional Intake and Health Status, with a Statistical Control for Age SW 540

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1 Using Control Variables Examining the Relationship Between Nutritional Intake and Health Status, with a Statistical Control for Age SW 540 Data. We have 8 observations with the following information, with measures for nutritional intake, health status, and age. Nutritional Intake Health Status Age : No control for age a. Enter Summary.794 a C:\WP60_\LECT.PHD\OLSReg+Corr\Control Variables 3.doc

2 a a From this, we see that there is a negative relationship between nutritional intake and health status, a counterintuitive result. We need to control for alternative hypotheses, such as age having an effect on health. Before we do that, let s see what the relationship is between nutritional intake and health within each of our different age categories. 2: 20 year olds only. a. Enter Summary.848 a C:\WP60_\LECT.PHD\OLSReg+Corr\Control Variables 3.doc 2

3 a a There is a positive relationship between our IV (independent variable) and our DV (dependent variable) in this case. 3. 3, examining only 50 year olds. a. Enter Summary.89 a C:\WP60_\LECT.PHD\OLSReg+Corr\Control Variables 3.doc 3

4 a a We again find a positive relationship between the IV and the DV. 4: only examining the 70 year olds. a. Enter Summary.994 a C:\WP60_\LECT.PHD\OLSReg+Corr\Control Variables 3.doc 4

5 a a Again, a positive relationship between the IV and the DV. Thus, in each of our bivariate models, we ve found a positive relationship between the IV and the DV but in the case where we use all the observations we find a negative relationship between the IV and the DV. Next, we will control for age and use all the observations to examine the true relationship between nutritional intake and health status. 5: Examining the effects of nutritional intake on health status, controlling for age. Variables Entered Variables Removed Method AGE, a. Enter Summary.97 a a. Predictors:, AGE, C:\WP60_\LECT.PHD\OLSReg+Corr\Control Variables 3.doc 5

6 a a. Predictors:, AGE, AGE a B Std. Error Beta t Sig Here we find that nutritional intake has a positive relationship with health status once we control for age. Age has a negative relationship with health, controlling for nutritional intake. We can look to see if there is a relationship between age and nutritional intake: AGE Correlations Pearson Correlation Sig. (2-tailed) N Pearson Correlation Sig. (2-tailed) N AGE.988** ** **. Correlation is significant at the 0.0 level (2-tailed). This indicates that there is a strong positive relationship between the two variables. Failing to include a relevant variable from the regression model that is correlated with the included variables in the model will give biased b coefficients. C:\WP60_\LECT.PHD\OLSReg+Corr\Control Variables 3.doc 6