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GCH 412
Homework 8
Experimental Studies
(and maybe other designs)
Clostridium difficile, often called C. difficile or “C. diff,” is a bacterium that can cause a wide variety of
gastro-intestinal symptoms ranging from diarrhea to life-threatening inflammation of the colon. C. diff most
commonly affects older adults in hospitals or in long term care facilities and typically occurs after the use of
antibiotic medications. C. diff bacteria are passed in feces and spread to food, surfaces, and objects when
people who are infected don’t wash their hands thoroughly. The bacteria produce hardy spores that can
persist in a room for weeks or months, thus it is easily spread.
A local hospital noticed an increase in nosocomial infections of C. diff in their elderly patient population. A
study was conducted to determine whether a new anti-bacterial hand soap was more effective than the
current hand soap in preventing the occurrence of C. diff infections. Elderly patients on the cardiac intensive
care floor were assigned to the new hand soap intervention and elderly patients on the general intensive care
floor were assigned to the usual hand soap regimen. All staff members and visitors were instructed on
proper hand washing techniques before they were permitted to see patients. Over the 6-month span of the
intervention, there were 3 C. diff infections among the 212 patients in the new hand soap intervention. There
were 32 C. diff infections in the 243 patients in the usual hand soap group.
Complete the 2×2 table for these data. Be sure to label the boxes properly.
1. Is this an experimental study? Why or why not?
2. Is this a randomized controlled study? Why or why not?
3. What is the appropriate measure of association for this type of study? Calculate and interpret it in
words.
4. You should have some concerns with how this study was conducted. What concerns do you have
and how would you address them? Please provide two suggestions. This is an open-ended question
without definitively right and wrong answers; I just wanted to get you thinking about all the potential
issues with the conduct of this study.
Pertussis, or whooping cough, is a highly contagious bacterial disease caused by Bordetella pertussis or
Bordetella parapertussis bacteria that cause uncontrollable, violent coughing. The coughing can make it
hard to breathe. A deep “whooping” sound is often heard when the patient tries to take a breath. It is a
serious disease that can cause permanent disability in infants, and even death. When an infected person
sneezes or coughs, tiny droplets containing the bacteria move through the air, and the disease is easily
spread from person to person. An outbreak of pertussis recently occurred in the state of California, resulting
in the deaths of several infants. DTaP vaccination, one of the recommended childhood immunizations,
protects children against pertussis infection. DTaP vaccine can be safely given to infants. As the immunity
from vaccines wears off over time and pertussis booster vaccine rates in adolescents and adults continue to
be low, researchers wished to evaluate the efficacy of a new vaccine requiring only one booster at age 7
against the current vaccine which requires 5 doses at ages 2 months, 4 months, 6 months, 15-18 months, and
4-6 years and a booster at age 11.
The new vaccine was used to vaccinate 545 children with 26 children developing whooping cough over the
next five years. The current vaccine was used to vaccinate 550 children with 37 children developing
whopping cough over the next five years. Please complete the 2×2 table with these data. Be sure to properly
label your exposure and outcome.
1. What type of study is this? How do you know?
2. State and calculate the appropriate measure of association. Interpret this information in words.
3. Can you calculate AR%? If so, please calculate and explain your results. If not, explain why it cannot be
calculated.
Spasmodic dysphonia (SD) is an idiopathic, chronic, and disabling voice disorder. Researchers were
interested in investigating the relationship between SD and meningitis. 150 individuals suffering from SD
and 150 individuals without SD were identified for a study. Of those with SD, 16 had previously had
meningitis. Of those without SD, 3 had previously experienced meningitis. Complete the following 2×2 with
this information. Be sure to properly label your exposure and outcome.
1. What type of study is this? How do you know? Be precise.
2. State and calculate the appropriate measure of association. Interpret this information in words.
3. Can you calculate AR%? If so, please calculate and explain your results. If not, explain why it
cannot be calculated.
Researchers were interested in the relationship between hypertension (defined as blood pressure of 140/90
mm HG or higher) and coronary heart disease (CHD). Participants were recruited between 1995 and 1997
and consisted of 1,333 male and 1,661 female residents of Mason County aged 28-62 years old. Of these
participants, 1295 had high blood pressure; the rest did not. Participants did not have heart disease at the
beginning of the study and all participants were followed for six years. In the group that initially had high
blood pressure, 106 individuals developed coronary heart disease. In the group with normal blood pressure,
1655 showed no signs of CHD. Complete the following 2×2 with this information. Be sure to properly label
your exposure and outcome.
1. What type of study design is this? How do you know?
2. State the appropriate measure of association. Calculate it and interpret it in words.
3. Can you calculate an AR%? If so, calculate and explain it. If not, explain why it cannot be
calculated.
According to the CDC, kidney disease occurs when the kidneys become damaged and lose their ability to
filter the blood. Left untreated, kidney disease can lead to kidney failure. People with severe kidney failure
must undergo dialysis or have a kidney transplant to stay alive. More than eight million Americans have a
major loss in kidney function. Of those, nearly 400,000 require dialysis or a kidney transplant to stay alive.
Diabetes is the leading risk factor for kidney disease. Researchers went to a local diabetes awareness event
and asked participants whether they had ever been diagnosed with kidney disease and whether they
currently had diabetes. There were a total of 2,000 participants at the fair. Of these, 1280 had diabetes and
the rest did not. In the group with diabetes, 166 had kidney disease. In the group without diabetes, 677 did
not have kidney disease. Complete the following 2×2 with this information. Be sure to properly label your
exposure and outcome.
1. What type of study design is this? How do you know?
2. What is the appropriate measure of association? Compute it and interpret it in words.
3. Can you calculate an AR%? If so, calculate and explain it. If not, explain why it cannot be
calculated.
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