Naleid and colleagues (2008) asked how the interaction of the ingredients corn oil and sucrose enhanced liking for vanilla milkshakes. To test this, rats responded on a lever to gain access to sucrose alone and to gain access to sucrose mixed with corn oil. The researchers hypothesized that rats would work harder (respond with a higher rate of lever pressing) for the mixture compared with sucrose alone. They found that adding 1.4% corn oil to a 12.5% sucrose solution enhanced liking (increased responding on the lever) compared to 12.5% sucrose alone, p < .01.
(a) Is this a repeated-measures design or a matched-pairs design?
(b) Did these authors find support for their hypothesis?