Answer because bagels and cream cheese are often eaten together, they are complements.
a. we observe that both the equilibrium price of cream cheese and the equilibrium quantity of bagels have risen. what could be responsible for this pattern— a fall in the price of flour or a fall in the price of milk? illustrate and explain your answer.
b. suppose instead that the equilibrium price of cream cheese has risen but the equilibrium quantity of bagels has fallen. what could be responsible for this pattern— a rise in the price of flour or a rise in the price of milk? illustrate and explain your answer.

Reliability and validity reliability and validity are two important considerations that must be made with any type of data collection. reliability refers to the ability to consistently produce a given result. in the context of psychological research, this would mean that any instruments or tools used to collect data do so in consistent, reproducible ways. unfortunately, being consistent in measurement does not necessarily mean that you have measured something correctly. to illustrate this concept, consider a kitchen scale that would be used to measure the weight of cereal that you eat in the morning. if the scale is not properly calibrated, it may consistently under- or overestimate the amount of cereal that’s being measured. while the scale is highly reliable in producing consistent results (e.g., the same amount of cereal poured onto the scale produces the same reading each time), those results are incorrect. this is where validity comes into play. validity refers to the extent to which a given instrument or tool accurately measures what it’s supposed to measure. while any valid measure is by necessity reliable, the reverse is not necessarily true. researchers strive to use instruments that are both highly reliable and valid.