Assume that firms in a perfectly competitive market are earning economic profits. which of the following statements describes the change in market price and output as a result of the entry of new firms into this market?
a) the short - run market supply curve shifts to the right, causing price to fall and total market output to increase.
b) the short - run market supply curve shifts to the left, causing price to fall and total market output to increase.
c) the market demand curves shifts to the left, causing price to fall and market output to decrease.
d) the market demand curves shifts to the right, causing price to fall and market output to increase.

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.