STAT 320: BIOSTATISTICS
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STAT 320: BIOSTATISTICS
Probability distributions
1. Diskin et al. (2003) studied common breath metabolites such as ammonia, acetone, isoprene, ethanol, and acetaldehyde in five subjects over a period of 30 days. Each day, breath samples were taken and analyzed in the early morning on arrival at the laboratory. For subject A, a 27-year-old female, the ammonia concentration in parts per billion (ppb) followed a normal distribution over 30 days with mean 491 and standard deviation 119. What is the probability that on a random day, the subject’s ammonia concentration is between 292 and 649 ppb?
2. The Uptimer is a custom-made lightweight battery-operated activity monitor that records the amount of time an individual spends in the upright position. In a study of children ages 8 to 15 years, Eldridge et al. (2003) studied 529 normally developing children who each wore the Uptimer continuously for a 24-hour period that included a typical school day. The researchers found that the amount of time children spent in the upright position followed a normal distribution with a mean of 5.4 hours and standard deviation of 1.3 hours. Assume that this finding applies to all children 8 to 15 years of age.
(a) Find the probability that a child selected at random spends less than 3 hours in the upright position in a 24-hour period.
(b) In a population of 10,000 children, how many would you expect to be upright more than 8.5 hours?
3. Suppose the average length of stay in a chronic disease hospital of a certain type of patient is 60 days with a standard deviation of 15. If it is reasonable to assume an approximately normal distribution of lengths of stay, find the probability that a randomly selected patient from this group will have a length of stay:
(a) Greater than 50 days
(b) Less than 30 days
(c) Between 30 and 60 days
(d) Greater than 90 days
4. According to a June 2003 poll conducted by the Massachusetts Health Benchmarks project, approximately 55 percent of residents answered “serious problem” to the question, “Some people think that childhood obesity is a national health problem. What do you think? Is it a very serious problem, somewhat of a problem, not much of a problem, or not a problem at all?” Assuming that the probability of giving this answer to the question is 0.55 for any Massachusetts resident, what is the probability
that if 10 residents are chosen at random:
(a) Exactly seven will answer “serious problem”
(b) Five or fewer households will answer “serious problem”
(c) More than five households will answer the “serious problem”
5. The probability of experiencing moderate to severe side-effects with a new drug is 0.03. If 200 people take the new drug, what is the probability that more than 8 people will experience moderate to severe side-effects?
6. In a study of drug-induced anaphylaxis among patients taking rocuronium bromide as part of their anesthesia, Laake and Røttingen (2001) found that the occurrence of anaphylaxis followed a Poisson model with 入 = 12 incidents per year in Norway. Find the probability that in the next year, among patients receiving rocuronium at least three will experience anaphylaxis.
2023-05-19
Probability distributions