Ted makes five paper airplanes with different wing lengths. He drops them from a height of eight feet for four trials each. He records the amount of time it takes for each airplane to fall to the ground. The independent variable (IV) is _____, the dependent variable (DV) is _____ and the control variable is _____.

Question 13 options:

	height at which airplanes are dropped; time to fall to the ground; wing length
	time to fall to the ground; wing length; height at which airplanes are dropped
	wing length; time to fall to the ground; height at which airplanes are dropped
	wing length; height at which airplanes are dropped; time to fall to the ground

Question 14 (1 point)

If a study describes the "difference in differences," what is the minimum number of independent variables the researchers were studying?

Question 14 options:

	4
	2
	3
	1

Question 15 (1 point)

A researcher is studying spatial learning in young learners following the participation in two different teaching interventions. The researcher is worried that her participants will have higher scores for their spatial learning performance following the second intervention because of their previous exposure to the test following the first intervention. What type of validity is the researcher concerned about?

Question 15 options:

	Statistical validity
	Internal validity
	Construct validity
	External validity

Question 16 (1 point)

Suppose Dr. In-n-Out Burger is conducting a study in which he manipulates how much salt is used when cooking the burgers and measures participants' ratings of how good the burgers taste on a 1 to 10 scale. Dr. Burger randomly assigned participants to one of three salt conditions: low salt, medium salt, and high salt. Everything else was held constant. He found that there was a significant relationship between the amount of salt and the taste rating. Which of the three causal criteria does this study meet?

Question 16 options:

	It meets covariation, temporal precedence and internal validity.
	It only meets covariation.
	It only meets covariation and internal validity.
	It only meets covariation and temporal precedence.

Question 17 (1 point)

Which of the following is a reason that a study might result in a null effect?

Question 17 options:

	too much variance between groups
	not enough variance within groups
	the IV truly affects the DV
	none of these are reasons for a null effect

Question 18 (1 point)

Dr. Gong conducts a study where she randomly assigns participants to different experimental conditions. The testing for each condition occurs in a different room of the psychology building. After collecting her data, she learns that the air conditioning in one of the rooms had been turned off during data collection. Which of the following threats to internal validity should Dr. Gong be concerned with?

Question 18 options:

	design confound
	maturation effect
	order effect
	selection effect