A florist wants to determine if a new additive would extend the life of cut flowers longer than the original additive. The florist randomly selects 20 carnations from the ones recently delivered by the greenhouse and places the first 10 in water with the new additive and remaining 10 in water with the original additive. After three weeks, 6 carnations placed in the new additive still looked healthy and 2 carnations placed in the original additive still looked healthy. The proportion of healthy carnations with the new additive was significantly greater than the proportion of healthy carnations with the original additive.
Answer
A
Conclusions about cause and effect for the additives can be made, because the florist randomly selected the 20 carnations; additionally, inferences can be made about the population of carnations at the greenhouse.
B
Conclusions about cause and effect for the additives cannot be made, because the florist did not randomly assign the 20 carnations; however, inferences can be made about the population of carnations at the greenhouse, because the sample was random.
C
Conclusions about cause and effect for the additives can be made, because the florist took a random sample of 20 carnations; however, inferences cannot be made about the population of carnations at the greenhouse, because the carnations were not randomly assigned to the treatments.
D
Conclusions about cause and effect for the additives cannot be made, because the florist took a random sample of 20 carnations; and, inferences cannot be made about the population of carnations at the greenhouse, because the carnations were not randomly assigned to the treatments.
Explanation
The florist randomly sampled 20 carnations, so the results can support inferences about carnations from that greenhouse. But the treatments were not randomly assigned: the first 10 received the new additive and the remaining 10 received the original additive, so differences between the groups could be due to something other than the additives. Thus, a cause-and-effect conclusion is not justified. Choice B correctly distinguishes the random sample from the lack of random assignment.
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