SECTION A
1
(a) A food manufacturer employed a research group to assess whether
supplementing children’s diet with DHA (an Omega-3 fatty-acid) would affect
their ablity to sustain attention at school. To measure sustained attention, a task
was devised in which children had to press a key whenever a small triangle was
presented on a computer screen, but not to respond when other shapes were
presented. The stimuli were presented one at a time at random locations on the
screen. Target stimuli remained on the screen until a response was made.
Average reaction time for responses to triangles over a twenty-minute period was
recorded for each child.
Prior to performing the task, forty children were randomly assigned to one
of two groups. Every day for four weeks, children from one group each received a
tablet containing DHA and those from the other group received a placebo. You
may assume that the children could not distinguish the DHA tablet from the
placebo tablet, that the two groups did not differ in terms of the number of errors
they made, and that reaction times for each group were normally distributed.
GROUP Reaction Time GROUP Reaction Time
(milliseconds) (milliseconds)
DHA 595 PLACEBO 588
DHA 532 PLACEBO 637
DHA 672 PLACEBO 574
DHA 574 PLACEBO 553
DHA 476 PLACEBO 448
DHA 651 PLACEBO 525
DHA 504 PLACEBO 511
DHA 546 PLACEBO 644
DHA 511 PLACEBO 609
DHA 658 PLACEBO 693
DHA 637 PLACEBO 581
DHA 546 PLACEBO 441
DHA 553 PLACEBO 504
DHA 581 PLACEBO 525
DHA 532 PLACEBO 609
DHA 574 PLACEBO 518
DHA 693 PLACEBO 483
DHA 609 PLACEBO 476
DHA 532 PLACEBO 539
DHA 588 PLACEBO 518
Did the DHA supplements have a significant effect on performance of the
sustained attention task?
TURN OVER
(b) In a second study, the same research group studied whether prolonged use
of DHA supplements in identified ‘at risk’ pre-school children affected the
probability of a child later being diagnosed with Attention Deficit Disorder
(ADD). One hundred children were randomly assigned to one of two groups; each
child in the first group of fifty received a DHA tablet and each from the other
group received a placebo. Again, you may assume that the tablets were
indistinguishable from each other. In the control group 28 of the 50 children were
later diagnosed with ADD, whereas in the DHA group, 18 of the children received
diagnoses.
Did the DHA tablets affect significantly the likelihood of a ADD diagnosis?
c) Finally, the research group wished to examine performance on the
sustained attention task prior to receiving DHA tablets versus after receiving
DHA tablets. A group of twenty children are tested on the task described in
Question 1a. They then receive DHA tablets each day for three weeks and are
then re-tested on the same task. What statistical test should be used to examine
whether or not performance improved following administration of DHA tablets?
SECTION B
2 Design an experiment to assess whether patients process emotional aspects
of stimuli while under general anaesthesia.
3 Design an experiment to test whether or not one year old human infants
distinguish short-term properties (e.g., direction of motion, emotion) from
more permanent long-term properties (e.g., identity, gender) of other
people.
4 Testosterone levels can be measured in samples of amniotic fluid during
pregnancy. A scientist claims that foetuses who have high levels of
testosterone in amniotic fluid will later develop poor face processing in
adulthood. Design a study to examine this claim.