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Stats Chapter 3 & 4
Contributed by: Lehnert

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.

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