1 A researcher wishes to use an observational study to determine the proportion of drivers who do not stop at a stop sign, depending on how much traffic is in the area at the time. The researcher stays hidden, using cameras and sensors, during times when traffic is light and when it is heavy. After observing for two weeks and analyzing the data, the researcher discovers that drivers stop at stop signs 95% of the time when the traffic flow is heavier than one car per minute. He concludes that an increase in traffic flow causes drivers to stop at stop signs. Is it correct for the researcher to draw this causation between traffic flow and whether drivers stop at stop signs?

Yes, he is correct, because the number of drivers who do not stop at stop signs increases as the traffic flow lightens.

Yes, he is correct, because the heavier the traffic flow, the more likely the driver is to stop at a stop sign based on the proportion 95%.

No, he is incorrect, because the researcher used an observational study, and therefore no causation can be drawn.

No, he is incorrect, because the study was only conducted by one researcher.

2 A scientist has a hypothesis that as the number of police cars is increased on a roadway, the proportion of cars speeding decreases. He finds that at police car level X1(one police car per 100 miles), the proportion of cars speeding is p=0.83. At police car level X2(one police car per 50 miles), the proportion of cars speeding is p=0.61. At police car level X3(one police car per 25 miles), the proportion of cars speeding isp=0.39 . Should the hypothesis be rejected or should it fail to be rejected?

Rejected, because the data do not support the hypothesis that as the number of police cars per mile increases, the proportion of cars speeding decreases

Fail to be rejected, because this was an experimental study and the hypothesis is always confirmed in this form of study

Fail to be rejected, because the proportion of drivers speeding goes down as the number of police cars per mile on a roadway increases

Rejected, because one of the limits of an experimental study such as this is that causation cannot be made between the variables

3 The band instructor at a local high school is timing his trumpet players to determine how long they can play a note without taking a breath. The average time is 56 seconds. What type of study is this?

Experimental study

Observational study

Nonrandomized study

Sample survey