Bill youngdahl has been collecting data at the tu student grill. he has found that, between 5: 00 p. m. and 7: 00 p. m., students arrive at the grill at a rate of 20 per hour (poisson distributed) and service time takes an average of 2.0 minutes (negative exponential distribution). there is only 1 server, who can work on only 1 order at a time. a. what is the average number of customers in line?

b. the average time in minutes in the system?

c. suppose that a second server can be added to team up with the first (and, in effect, act as one faster server). this would reduce the average service time to 90 seconds. the average time in the system in minutes is?

d. suppose a second server is added and the 2 servers act independently, with each taking an average of 2.0 minutes. if a second teller is added, the average time a customer spends in the system in minutes is?

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.