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Does using a cell phone while driving make an accident more likely? Researchers compared telephone company and police records to find 699 people who had cell phones and were also involved in an auto accident. Using phone billing records, they compared cell phone use in the period of the accident with cell phone use the same period on a previous day. Result: the risk of an accident was 4 times higher when using a cell phone.
This study is a randomized comparative experiment an experiment, but without randomization. a simple random sample an observational study, but not a simple random sample Does using a cell phone while driving make an accident more likely? Researchers compared telephone company and police records to find 699 people who had cell phones and were also involved in an auto accident. Using phone billing records, they compared cell phone use in the period of the accident with cell phone use the same period on a previous day. Result: the risk of an accident was 4 times higher when using a cell phone.
The explanatory variable in this study is whether or not the subject had an auto accident. whether or not the subject was using a cell phone. the risk of an accident. whether or not the subject owned a cell phone. You are designing a clinical trial to see whether added calcium in the diet will reduce the blood pressure of middle-aged men. You plan to give added calcium to a group of men and see whether their blood pressure is lower after six weeks. If you don't include a control group, your data will be invalid because of: the placebo effect lack of confidentiality the double-blind effect voluntary response the authors of the study must agree to inform the public of the study results. a review board must agree that the study is worthwhile and will not harm the subjects. the authors of the study must inform a review board about it and obtain the board's consent to go ahead. the nature of the study must be explained in advance to the subjects and they must voluntarily agree to take part. Any statistical study that uses human subjects requires informed consent. This means that A study at Yale Medical School investigated treatments for chronic cocaine abusers. Of the 72 subjects, all cocaine users who wanted to quit, 24 were assigned at random to each of three drugs: (a) desipramine, (b) lithium, (c) a placebo. After 6 weeks the subjects reported whether they had stayed off cocaine.
The response variable in the Yale study is whether or not a subject stayed off cocaine. which drug a subject was given 72 cocaine users. randomization. You measure the age, marital status, and earned income of an SRS of 1463 women. The number of variables you have measured is 1463 -- the size of the sample four -- age, marital status, income, and number of women three -- age, marital status, and income two -- age and income. Marital status is not a variable because it doesn't have a unit like years or dollars The 70th percentile of a distribution is the number with 70% of the data below it the number with 70% of the data above it the number that is 70% of the average 70% of the sample size The standard deviation should not be used to measure spread when the distribution is normal the mean is used to measure center the distribution is symmetric the distribution is skewed The possible values of the standard deviation s of a set of observations are: s can be any number, positive, 0, or negative s can be 0 or positive, but not negative s can be positive, but not 0 or negative s must be between -1 and 1. You calculate that the standard deviation of a set of observations is 0. This tells you that you made an arithmetic mistake all the observations have the same value. the mean must also be 0 Both (b) and (c) are true. |