A report on the 1995 National Health Risk Behavior Survey, conducted by the Centers for Disease Control and Prevention, can be found at the CDC website [www.cdc.gov: More Data & Statistics: CDC Data & Statistics Resources, Surveys Tab: CDC Surveys, Youth Risk Behavior Surveillance System (YRBSS): Publications and Data Files, YRBSS Publications: MMWR: Youth Risk Behavior Surveillance - National College Health Risk Behavior Survey - United States, 1995, or, directly, go to www.cdc.gov/mmwr/PDF/ss/ss4606.pdf]. Among the issues addressed in the survey was whether the subjects had, in the prior 30 days, ridden with a driver who had been drinking alcohol. Does the proportion of students exhibiting this selected risk behavior vary by ethnic group? The report includes tables summarizing the "Ridden Drinking" risk behavior by ethnic group (Table 3) and the ethnic composition (Table 1) for a sample of n = 4,609 college students. The "Ridden Drinking" and ethnic group information is extracted from Tables 1 and 3 and is displayed as proportions or probabilities in the leftmost panel of the table below. Note that the values in the body of the leftmost panel are given as conditional probabilities, the probabilities of exhibiting the "Ridden Drinking" risk behavior, given ethnic group. These conditional probabilities can be multiplied by the appropriate marginal probabilities to compute the joint probabilities for all the risk behavior by ethnic group combinations to obtain the summaries in the center panel. Finally, the joint probabilities are multiplied by the sample size to obtain projected counts for the number of students in each "Ridden Drinking" by ethnic group combination. The "Other" ethnic group was omitted from the Table 3 summaries and is thus not included in this analysis.
Is there sufficient evidence to conclude that the proportion of college students exhibiting the "Ridden Drinking" behavior varies by ethnic group? Conduct a chi-square test for independence using the projected count data provided in the rightmost panel of the summary table. (Data are available in MINITAB and Excel files, YouthRisk.mtw and YouthRisk.xls.) Test at the 0.01 level of significance and report an approximate p-value for your test. Be sure to clearly state your hypotheses and conclusion.

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Conditional Probabilities [Table 3: P(R E). Table 1: P(E)] Joint Probabilities [P(ER) P(R E)P(E)] Projected Counts In 46091 In(ER) P(ER) x 4609] Ridden Drinking? Ridden Drinking? Ridden Drinking? Ethnic White Total %YEth 0.383 0.275 %NEth 0.617 0.725 0.693 % Ethnic 0.728 0.103 0.071 Yes 0.2788 0.4492 0.7280 1,285 2,070 0.0283 0.0747 0.0218 Yes No Total 3,355 475 327 No 131 100 344 227 Black Hispanic 307 0.1030 0.0710 0.0492