009 o Or 09 Relative Risk Relative risk is a ratio of the probability of the

009 o or 09 relative risk relative risk is a ratio of

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Death rate is 0.009 o Or 0.9% Relative Risk Relative risk is a ratio of the probability of the event occurring in the exposed group versus a non-eposed group = probablility in exposed group/probability in unexposed Risk CV disease- present CV disease- absent Overweight A (20) B (80) Normal weight C (2) D (100) = (a/(a+b))/(c/(c+d)) 100 overweight 102 normal weight 1. Probability in exposed- 20/(20+80) = .2 2. Probability in unexposed- 20/(102)= .02 a. Determine the ratio- 10 b. Interpret: overweight are 10 times more likely to develop CVD than normal weight
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Relative risk interpretation What does it mean if RR = 1 o There is no difference in risk between the exposed and the unexposed group What does it mean if the RR in the exposed group is <1? o I.e. RR for CVD in physically active people is .6 compared with inactive people (RR=1) What does it mean if the RR in the exposed group is >1? o Percent relative risk When RR in the exposed group is >1? o % increase = (RR-1) x 100 o I.e. RR of 3.5 = (3.5-1) x 100 = 250% greater risk for CVD in smokers compared to non- smokers When RR in the exposed group is <1? o % decrease = (1-RR) x 100 o RR of 0.6 = (1-.6) x 100 = 40% lower risk for CVD in active people compared to inactive people Other terms Odds ratio - the ratio of the odds of an event occurring in one group to the odds of it occurring in another group o Used in studies where two groups are compared (cases and controls) o Odds in cases Odds in controls o =1 – no association o >1 – positive association o <1 – negative association Hazard ratio - used when the mortality is the outcome o Different from RR o HR is an instantaneous risk over study period o RR is cumulative over the study period The ratio of the probability of an event (death or progression) in the experimental arm vs. control arm of a study o Similar to incidence rate o incidence rate exposed group/incidence rate unexposed group Population attributable risk Incidence of disease or other health outcome in a population that can be attributed to exposure to particular risk factor o Information about which exposure is most powerful for health in population
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Calculation of person-time years You do a study with 5 subjects and follow them for 5 years o If everyone completed that would be 25 person-years (5x5) (above chart): started late, counts 4 years. Gets disease, stops counting. Never gets disease, counts full 5 years. 9/16 Why is measurement important? Determine “dose” of physical activity that is important for health Determine population levels of physical activity and how they change over time Determine if interventions to increase physical activity improve health
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Why are we interested in energy expenditure? Understand metabolic requirements for rest and exercise Energy balance Physical activity assessment Monitor energy expenditure Energy expenditure - the amount of energy a person uses daily to complete all bodily activities Energy balance (energy intake- over/under eating, energy expenditure- physical activity/sedentary behavior)
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  • Fall '15
  • physical activity

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