Question

lucy designed an experiment to investigate whether listening to music or burning a scented candle affects her performance while playing her favorite video game. each day for one month, she randomly chose whether to listen to classical, rock, or no music while playing her favorite video game. each day, she also randomly chose whether to burn a candle with an orange scent, burn a candle with a lavender scent, or not burn a candle. at the end of each day, she recorded the mean score for 10 plays of her favorite video game.
how many explanatory variables are in the experiment?
a. one
b. two
c. three
d. six
e. nine

in order to determine if smoking causes cancer, researchers surveyed a large sample of adults. for each adult they recorded whether the person had smoked regularly at any period in his or her life and whether the person had cancer. they then compared the proportion of cancer cases for both groups. the researchers found there was a higher proportion of cancer cases among those who had smoked regularly than among those who had never smoked regularly.
this is:
a. a block design
b. an observational study
c. an experiment but not a double - blind experiment
d. a double - blind experiment
e. a single blind experiment

which of the following can be used to show a cause - and - effect relationship between two variables?
a. a census
b. a controlled experiment
c. an observational study
d. a sample survey
e. a simple random sample

a well - designed experiment should have which of the following characteristics?
i. subjects assigned randomly to treatments
ii. a control group or at least two treatment groups
iii. replication
a. i only
b. i and ii only
c. i and iii only
d. ii and iii only
e. i, ii, iii

Explanation:

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Step1: Identify explanatory variables

Explanatory variables are factors manipulated in an experiment. Here, music - 3 options (classical, rock, no music) and candle - 3 options (orange scent, lavender scent, no candle) are manipulated.

Step2: Count number of types of manipulation

There are two types of manipulation: music and candle, so 2 explanatory variables.

In this case, researchers just surveyed and compared proportions without manipulating any variables. This is an observational study as they did not assign treatments (smoking or not) to the subjects.

A controlled experiment is the only method among the options that can show a cause - and - effect relationship. In a controlled experiment, one variable is manipulated while others are controlled, allowing for determination of cause - and - effect.

Answer:

b. two

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