Use this description of a research study to answer the questions that follow:

A researcher conducted a study to examine when students would be more likely to look for oncoming traffic when crossing a street. The researcher predicted that students would be less likely to look for oncoming traffic when crossing at an intersection with a designated crosswalk (i.e., with lines marking the crossing) than when crossing at an intersection without a designated crosswalk (i.e., no lines). A team of six student researchers made the observations for this study. The observers made their observations on Monday, Wednesday, and Friday for one week, and on Tuesday and Thursday during a second week. On each day, they observed the intersections for one hour mid-morning and for one hour mid-afternoon. Both intersections were observed during each observation session. The observers were in a location such that they could see the intersections, but could not be seen by the pedestrians who were being observed. The observers included only student pedestrians who were walking alone, and they counted the student as having "looked for traffic" if he or she looked in one or both directions before entering the intersection. The observers made initial observations together to establish agreement regarding what constituted "looking for traffic." These observations were not included in the final data. Over 200 students were observed crossing the intersection at the designated crosswalk and over 150 students were observed crossing at the intersection without the designated crosswalk. Their results supported the researcher's prediction: fewer students looked for traffic when crossing at the designated crosswalk than when crossing at the intersection without the designated crosswalk.

(1) What type of observational method was used in this study? Explain your answer.

(2) The students selected levels of an independent variable in their study. What is the operational definition of this variable?

(3) What measurement scale is used for their dependent variable? Explain your answer.

(4) What type of sampling did the observers use to decide when to make their observations? Briefly explain your answer.

(5) Identify one aspect of their procedure that likely increased the reliability of their observations.

(6) Identify one aspect of their procedure that likely decreased the problem of reactivity.

(7) Identify one aspect of their procedure that would likely limit the external validity of their findings.