Birth Length The mean birth length for U.S. children born at full term (after 40 weeks) is 52.2 centimeters (about 20.6 inches). Suppose the standard deviation is 2.5 centimeters and the distributions are unimodal and symmetric. (Source: www.babycenter.com) a. What is the range of birth lengths (in centimeters) of U.S.-born children from one standard deviation below the mean to one standard deviation above the mean? b. Is a birth length of 54 centimeters more than one standard deviation above the mean?
Birth Length The mean birth length for U.S. children born at full term (after 40 weeks) is 52.2 centimeters (about 20.6 inches). Suppose the standard deviation is 2.5 centimeters and the distributions are unimodal and symmetric. (Source: www.babycenter.com) a. What is the range of birth lengths (in centimeters) of U.S.-born children from one standard deviation below the mean to one standard deviation above the mean? b. Is a birth length of 54 centimeters more than one standard deviation above the mean?
Birth Length The mean birth length for U.S. children born at full term (after 40 weeks) is 52.2 centimeters (about 20.6 inches). Suppose the standard deviation is 2.5 centimeters and the distributions are unimodal and symmetric. (Source: www.babycenter.com)
a. What is the range of birth lengths (in centimeters) of U.S.-born children from one standard deviation below the mean to one standard deviation above the mean?
b. Is a birth length of 54 centimeters more than one standard deviation above the mean?
Definition Definition Measure of central tendency that is the average of a given data set. The mean value is evaluated as the quotient of the sum of all observations by the sample size. The mean, in contrast to a median, is affected by extreme values. Very large or very small values can distract the mean from the center of the data. Arithmetic mean: The most common type of mean is the arithmetic mean. It is evaluated using the formula: μ = 1 N ∑ i = 1 N x i Other types of means are the geometric mean, logarithmic mean, and harmonic mean. Geometric mean: The nth root of the product of n observations from a data set is defined as the geometric mean of the set: G = x 1 x 2 ... x n n Logarithmic mean: The difference of the natural logarithms of the two numbers, divided by the difference between the numbers is the logarithmic mean of the two numbers. The logarithmic mean is used particularly in heat transfer and mass transfer. ln x 2 − ln x 1 x 2 − x 1 Harmonic mean: The inverse of the arithmetic mean of the inverses of all the numbers in a data set is the harmonic mean of the data. 1 1 x 1 + 1 x 2 + ...
2. Hypothesis Testing - Two Sample Means
A nutritionist is investigating the effect of two different diet programs, A and B, on weight loss. Two
independent samples of adults were randomly assigned to each diet for 12 weeks. The weight losses (in kg)
are normally distributed.
Sample A: n = 35, 4.8, s = 1.2
Sample B: n=40, 4.3, 8 = 1.0
Questions:
a) State the null and alternative hypotheses to test whether there is a significant difference in mean weight
loss between the two diet programs.
b) Perform a hypothesis test at the 5% significance level and interpret the result.
c) Compute a 95% confidence interval for the difference in means and interpret it.
d) Discuss assumptions of this test and explain how violations of these assumptions could impact the results.
1. Sampling Distribution and the Central Limit Theorem
A company produces batteries with a mean lifetime of 300 hours and a standard deviation of 50 hours. The lifetimes are not normally distributed—they are right-skewed due to some batteries lasting unusually long.
Suppose a quality control analyst selects a random sample of 64 batteries from a large production batch.
Questions:
a) Explain whether the distribution of sample means will be approximately normal. Justify your answer using the Central Limit Theorem.
b) Compute the mean and standard deviation of the sampling distribution of the sample mean.
c) What is the probability that the sample mean lifetime of the 64 batteries exceeds 310 hours?
d) Discuss how the sample size affects the shape and variability of the sampling distribution.
A biologist is investigating the effect of potential plant
hormones by treating 20 stem segments. At the end of
the observation period he computes the following length
averages:
Compound X = 1.18
Compound Y = 1.17
Based on these mean values he concludes that there are
no treatment differences.
1) Are you satisfied with his conclusion? Why or why
not?
2) If he asked you for help in analyzing these data, what
statistical method would you suggest that he use to
come to a meaningful conclusion about his data and
why?
3) Are there any other questions you would ask him
regarding his experiment, data collection, and analysis
methods?
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