Because colas tend to replace healthier beverages and colas contain caffeine and phosphoric acid, researchers Katherine L. Tucker and associates wanted to know whether cola consumption is associated with lower bone mineral density in women. Table 4 lists the typical number of cans of cola consumed in a week and the femoral neck bone mineral density for a sample of 15 women. The data were collected through a prospective cohort study.

Figure 9 shows the scatter diagram of the data. The correlation between number of colas per week and bone mineral density is -0.806. The critical value for correlation with n = 15 from Table II in Appendix A is 0.514. Because 0 -0.806 0 7 0.514, we conclude a negative linear relation exists between number of colas consumed and bone mineral density. Can the authors conclude that an increase in the number of colas consumed causes a decrease in bone mineral density? Identify some lurking variables in the study.

Table II Appendix A

Approach To claim causality, we must collect the data through a designed experiment.
Remember, lurking variables are related to both the explanatory and response variables in a study.

Transcribed Image Text:

BMD Figure 9 0.895 0.890 0.885 0.880 Bone Mineral Density vs. Colas Consumed per Week 0.875 0.870 0.865 0.860 . T 0 2 -a T T 3 4 5 6 7 8 9 Colas