Memory has many different aspects (e.g. short term and long term) and
different tests have been developed to test these and other aspects of
memory. Researchers are interested in how anxiety and muscular tension
may affect memory in humans. 12 people are recruited to participate in
an experiment in which they will take four memory tests.

The participants are told that they will be rewarded monetarily. Each
one is first randomly assigned to one of two different
anxiety-producing reward structures. The supposedly higher anxiety
reward structure rewards participants $5 for participation but $100
if they remember sufficiently accurately on the tests. The lower
anxiety reward structure rewards participants $5 for participation
but $10 if they remember sufficiently accurately on the tests.

Each participant is then also randomly assigned to one of two
different muscular tension levels. While the tests are being taken,
each person must squeeze a spring loaded grip to prevent a buzzer from
sounding. The high-tension group must squeeze against a stronger
spring than the low-tension group.

The four memory tests are taken by each participant in a random order,
each one testing a different type of memory. The outcome is the number
of errors on each test.

These data are from Oehlert (2000), Example 16.5. Coding of anxiety and
tension is that 1 corresponds to the "low" level group and "2" 
corresponds to the high level group. The tests are shown in order of
memory type, not in order administered (which was random).