Studies have shown that people who suffer sudden cardiac arrest have a better chance of survival if a defibrillator shock is administered very soon after cardiac arrest. How is survival rate related to the length of time between cardiac arrest and the defibrillator shock being delivered? This question is addressed in the paper €œImproving Survival from Sudden Cardiac Arrest: The Role of Home Defibrillators€(www.heartstarthome. com). The accompanying data give y = survival rate (percent) and x = mean call to shock time (minutes) for a cardiac rehabilitation center (in which cardiac arrests occurred while victims were hospitalized and so the call to shock time tended to be short) and for four other communities of different sizes.

a. Find the equation of the least squares line.
b. Interpret the slope of the least squares line in the context of this study.
c. Does it make sense to interpret the intercept of the least squares regression line? If so, give an interpretation. If not, explain why it is not appropriate for this data set.
d. Use the least squares line to predict survival rate for a community with a mean call to shock time of 10 minutes.

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Mean call-to-shock time. x 2 6 7 9 12 79 12 Survival rate.y 90 45 30 S 2