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Biostatistics Practice2

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Example: A study shows that 70% of all patients coming to a certain medical clinic have to wait at least fifteen minutes to see their doctor. What is the probability that among ten patients coming to this clinic (a) 3 patients will wait (b) more than 8 patients will wait at least fifteen minutes to see their doctor? P(A) = p = 0,70 (a) (b)

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Example: The number of emergency calls which an ambulance service gets per day is a random variable having th Poisson distribution with . What is the probability that on any given day it will receive (a) only 4 emergency calls, (b) More than 4 emergency calls. (a) (b)

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Example: A group of patients have a mean body mass index (BMI) of 22 and a standard deviation 4. BMIs are approximately normally distributed. A subject is classified as obese if his BMI has greater than 30 BMI. In this group of patients what is the propotion of obese patients? What is the proportion of patients whose BMI less 18? =22 =4 0 z=2

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Example: It is known that 25% of the persons in the study were obese. In this study, 200 individuals were examined and mean BMI score was found as 23 and std. deviation was found as 5. What is the cut-off point for obesity? What is the number of the obese individuals? Number of obese individuals = 200*0,25 = 50

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Example: Scoring system was changed in ÖSS in 2003. The lowest score of the students who attended Hacettepe University School of Medicine was 195 in 2002, and 310 in 2003. It is also known that, in 2002 mean=160 & s=10, and in 2003 mean=270 & s=15. Has the attendance score increased in 2003?

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n=10 n=25 n=100 n=10 n=25 n=100 Sampling Distribution PercentPercent PercentPercent

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Example: If the mean and standard deviation of serum cholesterol values for male patients who was diagnosed as having myocardial infarction are 240 and 40 mg/dl, what is the probability that a random sample of 100 men will have a mean greater than 250 mg/dl?

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In the previous example, instead of 100 men, if we randomly select 16 men, what is the probability of obtaining a sample mean greater than 250 mg/dl?

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Example: A researcher wants to estimate the average serum cholesterol level of healty men. Mean and standart deviation of the randomly selected 100 men are 160 and 30 mg/dl. 95% CI for the population mean:

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When the researcher selected 36 men at random, 95% CI for the population mean: 90% CI for the population mean:

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Example: A researcher wants to estimate the prevalence of osteoporosis in women over fifty years of age. Among 100 randomly selected women, 15 women have a diagnosis of osteoporosis. What is the 95% confidence interval for the proportion of osteoporosis in women? Point estimate of the proportion of osteoporosis The standard error of the estimate is 0.036.

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95% CI for the population proportion If a researcher wants to calculate interval for the population proportion with 90% confidence:

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