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ENV 260/SDV 360 Independent Samples Design or Matched Pairs Dependent Smaples Design?
In each case, I describe a study that involves two samples. Determine if it is an independent samples
experimental design or a matched pairs design.
1. As part of a study of the physiology of wheat maturation, an agronomist selected six wheat
plants at random from a field plot. For each plant, she measured the moisture content in two
batches of seeds: one batch from the central portion of the wheat head and one batch from the
top portion. Dependent samples
2. Nutritional researchers conducted investigation of two high-fiber diets intended to reduce
serum cholesterol level. Twenty men with high serum cholesterol were randomly allocated to
receive an “oat” diet or a “bean” diet for 21 days. Independent samples
3. An entomologist conducted an experiment to see if wounding a tomato plant would induce
changes that improve its defense against insect attack. She grew larvae of the tobacco
hornworm (Manduca sexta) on 16 wounded plants and on 18 control plants. Independent
samples
4. Six patients with renal disease underwent plasmapheresis (removal of the plasma from the
blood). Urinary protein excretion (grams of protein per gram of creatinine) was measured for
each patient before and after plasmapheresis. Dependent samples
5. In a study of the effect of caffeine on muscle metabolism, nine male volunteers underwent arm
exercise tests on two separate occasions. On one occasion, the volunteer took a placebo
capsule an hour before the test; on the other occasion he received a capsule containing pure
caffeine. Dependent samples
6. In a very recent study, Duke professor Dan Ariely and colleagues at the Massachusetts Institute
of Technology, 82 study subjects were given one of two different brochures. One described the
medicine they were about to take as a newly approved pain killer costing $2.50 per dose, and
the other describing the medicine as marked down to 10 cents. Both "medicines" were actually
equivalent sugar pills. 85 percent of subjects experienced a reduction in pain if they took the
"expensive" pills; 61 percent of patients said their pain lessened if they took the "cheaper" pills.
Independent samples
7. A study was performed on the effect of introducing a low-fat diet on hormone levels of 73 postmenopausal women not using exogenous hormones. Plasma estradiol concentration in
picograms/milligram were measured pre- and post-intervention. Dependent samples
8. In 1876, Charles Darwin published a study on the concept of "hybrid vigor" entitled The Effect of
Cross- and Self-fertilization in the Vegetable Kingdom. In one of his experiments, pairs of
seedlings of Zea mays corn plants of the same age, one produced by cross-fertilization and the
other by self-fertilization, were grown together so that the members of each pair were reared
under nearly identical conditions. The aim was to demonstrate the greater vigor of the cross-
fertilized plants. The data are the final heights of each plant after a fixed period of time.
Dependent samples