A skill acquisition researcher is interested in examining the
effects of practice variability on learning of golf skills. She
aims to set up an experiment in her laboratory where she will
examine the effects of different practice schedules on a simulated
putting skills test. She proposes to have a total of 90
participants who will be randomly assigned into one of three
practice schedules. One group (n = 30) will complete the practice
trials according to a constant practice schedule [CP group] where
they will complete the 40 practice trials of the putting skill from
a distance of 3 meters. Another group (n = 30) will complete the
practice trials according to a variable practice schedule [VP
group] where they complete 40 practice trials of the putting skill
from four different distances (10 trials at each of 1, 3, 5 and 7
meter distances) in a random order. A third group (n = 30) will not
complete any practice trials – effectively a no practice schedule
[NP group]. Performance will be determined using a putting skill
test (10 putts) over a distance of 4 meters after participants have
completed the practice trials as per their group schedule. Each
putt is scored using a target grid with concentric circles marked
where 10 = ‘ball enters the hole (successful putt)’; 9 = ‘close to
the hole’ and so on through to 0 = ‘ball fails to land within
bounds of target grid’. The researcher aims to ensure that
conditions (e.g., temperature, lighting, noise) during the
experiment will be carefully controlled.
For the experiment described, identify
the following (make sure you number your responses to each of the
separate questions):
What is the independent variable?
What is the dependent variable?
How many levels of the independent variable are there?
What type of measure is the independent variable (i.e., what
measurement scale)?
What is the null hypothesis for the experiment (i.e., state the
null hypothesis)?
What is the alternative hypothesis for the experiment (i.e.,
state the alternative hypothesis)?
(10 marks)
Thinking further about the experiment described above (i.e., Q.
2). Before proceeding with the experiment, the researcher discusses
her proposed study with a colleague who has some concerns about the
design—specifically he questions the external validity of the
experiment. The researcher is prompted to reflect on the internal
and external validity of her proposed experiment.
What is meant by the term internal validity (briefly define)?
What is meant by the term external validity (briefly define)?
Explain how internal validity and external validity both affect the
quality of an experimental study.