Yeah, could someone also explain this please, because originally I thought that the study lacked in validity because the participants may have experienced performance impairment due to the experimental design of the study (repeated measures), especially on day 2 and 3. However the answers say to not only define it but state that the results are valid.
What answers are you using?
Also, I don't think that the question requires you to assess the experiment in terms of those terms, but rather just define them and put them into context. ie.
validity - refers to whether the procedure tested what the research intended to measure. eg. whether the effectiveness of the measurement of the mean number of driver errors is an accurate indicator of driver performance.
Reliability - refers to whether the results obtained are consistent and dependent over time. eg. whether other studies researched similar stuff came up with similar results, or if the procedure was repeated more times over the next couple of months would the results stay consistent...