Biostats Exam 2 HW Questions

The average BMI for a sample of 10 preschoolers is 16.1, with a standard deviation of 1.4. What is the 90% confidence interval for the BMI of all preschoolers?

(15.29, 16.91)

If in a sample of 355 adult males, we have a mean total cholesterol level of 185 mg, with s = 16. What is the 95% confidence interval for mean total cholesterol level of all males?

(183.34, 186.66)

What is the probability that a woman will have a height greater than 64.5 inches?

(64.5-63.6)/2.5 =.36 64.06-100 =35.94%

Given that the population of women's height has a mean of 63.6 inches and a standard deviation of 2.5 inches, answer the following questions: What is the z-score corresponding to a height of 70 inches?

(70-63.6)/2.5 =2.56

In a normal distribution with a mean of 78 and a standard deviation of 7, what is the probability that a score will be greater than 82?

(82-78)/7 =0.57 71.56-100 =28.43%

In a randomly selected sample of 500 Phoenix residents, 445 supported mandatory sick leave for food handlers. Legislators want to be very confident that voters will support this issue before drafting a bill. What is the 99% confidence interval for the percentage of Phoenix residents who support mandatory sick leave for food handlers?

(85.4%, 92.6%) -Ex 3 in ppt

What is the probability that a woman will have a height between 60 inches and 65 inches?

(Get probability percentages for both values and add them together) =63.74%

What is the range of height for 68% of women?

+/- one standard deviation 63.6+ 2.5= 66.1 63.6- 2.5= 61.1 -61.1-66.1

What is the critical value of a two-tailed test when alpha is .05 if the test statistic adheres to an asymptotic standard normal distribution.

+/-1.96

Which of the following is(are) true about confounding variables (choose one or more)?

-A confounding variable creates an association that is misleading. -A confounding variable is associated with the exposure. -A confounding variable is associated with the outcome.

Which of the following describe alpha? (choose one or more)

-A value we need to know in order to determine the critical value -The level of significance -The probability of the test statistic occurring if the null is true

Below is a hypothesis. There are 5 qualities of a good hypothesis outlined in our lecture. Which of the following apply to the hypothesis below? (choose one or more) Research hypothesis: A new mother's stress will go down when she uses her infant's nap time to engage in deep breathing and light exercise.

-Brief and to the point -Defines expected relationship between variables -Stated in declarative form rather than a question

Which of the following is/are formal procedure(s) for determining whether the result we obtained from our experiment is due to chance or not. (choose one or more)

-Compare test statistic to the critical value -Compare p-value to alpha

The purpose of the one-sample test is: (choose one or more)

-Compare two groups on a variable that is interval/ratio in measure -Determine the probability that two groups are the same with respect to a particular variable -To examine the difference between one group and a population

For which of the following scenarios would it be appropriate to use a one-sample z-test?

-Comparing the number of packs of cigarettes smoked per day by a sample of residents of rural areas with the number of cigarettes smoked per day by all persons in the USA -Comparing the average weight of newborns in Hospital A to the average weight of newborns in Hospital B

When using table B.1 in your text to determine the area under the curve which of the following are true? (choose one or more)

-If you need the area above a positive z score you have to subtract the area provided from 50 -The area between the mean and the z score is the same for a positive or negative z score -If you need the area below a negative z score you have to subtract the area provided from 50

Which of the following is/are true about the standard error of the mean? (choose one or more)

-It gets larger as sample size gets smaller -=population standard deviation divided by the square root of sample size -It is a measure of variance

What affects the width of a confidence interval? (choose one or more)

-Sample size. -Variation within the population. -Our desired confidence level.

Why do we need confidence intervals? (choose one or more)

-To give insight about the magnitude of the effect -To express statistical uncertainty -To accurately state a range of a population parameter

Under which condition(s) would you use a t-score instead of a z-score?

-Your sample size is less than 30 -You do not know the population standard deviation

Which of the following methods may be helpful in determining the area under the curve? (choose one or more)

-draw a diagram and shade the area of interest -Understand how to read your area under the curve table -Stick with one version of the area under the curve table

If you want to calculate a z score for a test where your individual score was 24, what other information must you know? (choose one or more)

-mean -standard deviation

What is the p-value for the one-sample z-test?

0.0044

You have a sample of 45 males, with an age range of 15-19, a mean height of 70.8 inches and a s of 1.5 inches. What is the standard error of the mean?

0.2236

In a normal distribution with a sample size of 45, a mean of 100, and a standard deviation of 15, what is the probability that a score will be 118 or higher?

11.51%

What is the test statistic?

2.26

For a sample with df = 5, what is the t-score constant to calculate a confidence level of 95%?

2.571

The constant used in calculating the 99% confidence interval in the proportion formula is:

2.576

When calculating the 99% confidence interval of the mean for a sample of 15 patients, what constant is used in the formula?

2.977

The average birthweight for babies in the United States is 3,325 grams with σ = 525. A researcher wishes to test whether or not a sample of 250 women in a rural community have a significantly different average birthweight than the national average at the α = 0.05 level. The mean birthweight for the sample of women in the rural community is 3400 grams. What is the degrees of freedom for this study?

249

In a normal distribution with a sample size of 60, a mean of 100 and a standard deviation of 15, what is the probability that a score will be 100 or lower?

50%

Under the normal curve, approximately what percent of scores fall between and -1 to +1 standard deviations around the mean?

68% -Empirical Rule

In a normal distribution with a mean of 78 and a standard deviation of 7, what is the probability that a score will be between 71 and 85?

68.26% -Zscores are -1 and 1 it is one SD away from the mean

If you hypothesize that there will be a difference between patient satisfaction scores from hospital A and hospital B, but you do not hypothesize the direction, you would have:

A non-directional research hypothesis

In this figure, the shaded areas represent _____ .(the very ends of the tails)

Area of rejection

If you want to explore the magnitude of the difference in the means between two groups, which measure of effect would you use?

Cohen's d

In order to determine whether or not you will reject the null hypothesis, the test statistic should be compared to which of the following?

Critical value

A hypothesis is basically a(n)

Educated guess

Sally wants to evaluate the level of attachment between mother and child pairs. She sets up a room with toys and books and observes the interactions between each mother and child pair. The air conditioner in the room is not working properly and the observation room is extremely hot. The temperature of the room is an example of ___________________.

Extraneous Variable

True or False, the alternative hypothesis states that there is no difference/no effect.

False

Which of the following symbols represents the null hypothesis?

H0

In the United States, mothers who live in poverty generally have babies with lower birthweight than women who do not live in poverty. The average birthweight for women living in poverty is 2800 grams, with a standard deviation of 500. Recently, a local hospital introduced an innovative prenatal care program to reduce the number of low birthweight babies born in the hospital. In the first year, 35 mothers, all of whom live in poverty, participated in this program. Program evaluators want to determine if the birthweight for infants of women who participated in the program is greater than the average birthweight for women who live in poverty. They choose an α of 0.05. The following data is the birthweight in grams for the babies born to the mothers who participated in this program How would you write the null hypothesis?

H0: xbar = 2800

Which of the following symbols represents the first research hypothesis?

H1

Which of the following represents a nondirectional research hypothesis?

H1: x bar1 ≠ x bar2

How would you write the alternative hypothesis?

Ha: m > 2800

As you increase your confidence level, what happens to the width of the confidence interval?

It gets wider

What is the term associated with how flat or peaked a distribution appears?

Kurtosis

A ________ is a statistic that measures the magnitude of the relationship between variables.

Measure of effect

If you hypothesize that there is only a positive or only a negative relationship between two variables, what type of test should you use?

One-tail

An endocrinologist has established group visits for her pregnant patients with diabetes. The average fructosamine level for patients who did not attend shared visits is 195. She hypothesizes that the average fructosamine level for patients who did attend shared visits will be lower. Would you use a one-tail test or a two-tail test to test this hypothesis?

One-tailed (specific)

If the mean of a set of scores is greater than the median, what can be said about the distribution?

Positively skewed

Researchers want to determine how many times per week people walk their dogs. They select a representative sample of 250 dog owners and ask them about their dog walking habits over the last year. What type of bias might be a problem?

Recall

In order to say that a distribution is positively skewed, which of the following must be true? (choose one or more)

Right tail must be longer than the left

A health-focused radio show wants to determine what percentage of people in the Phoenix area are taking cholesterol medication. They ask listeners to call in and report whether or not they are taking cholesterol medication. What type of bias might be a problem?

Selection

What does α represent?

Significance

Which of the following is a measure of how asymmetric your data is?

Skewness

In Excel functions, what does the output from the one-sample z-test represent?

The one-tailed probability value (p-value)

Which of the following statements about the p-value is true?

The p-value is the chance of getting an observed effect if the null hypothesis was true

Which of the following is not true about measures of effect?

They are affected by sample size

True or False, a finding can be statistically significant, but not clinically significant.

True

True or False, power is the ability of a study to find a difference if it actually exists.

True

True or False, the mean for a set of z scores is zero.

True

True or False, this finding is statistically significant at the α = .05 level.

True

True or False, this finding is statistically significant.

True

True or False, we always test a null hypothesis against an alternative hypothesis.

True

An endocrinologist has established group visits for her pregnant patients with diabetes. The average infant birthweight for patients who did not attend shared visits is 9.5 lbs. She hypothesizes that the average infant birthweight for patients who did attend shared visits will be different. Would you use a one-tail test or a two-tail test to test this hypothesis?

Two-tailed (nonspecific)

Which of the following occurs when you reject the null hypothesis when it is really true?

Type I Error

Researchers find that the 95% confidence interval for women's systolic blood pressure is (126.67, 127.93). How do you interpret this finding?

We are 95% confident that the true mean for women's systolic blood pressure is between 126.67 and 127.93.

If you know the z score (z), standard deviation(s) and mean (M), what formula would you use to compute the raw score (X)?

X = z(s) + M -Z score formula

When would you use the confidence interval formula for a proportion? (choose one or more)

You have summary information as a percentage or survey sample data

What is the Excel function for a one-sample z-test?

ZTEST

The probability of failing to reject a null hypothesis when it is false is represented by ______________.

beta (β)

Based on this information the researcher should conclude that pregnant women who live in poverty and participate in the prenatal care program have infants with ________ birthweights than women who live in poverty and do not participate in the program.

higher

When calculating confidence intervals in this class the product of a constant times a margin of error is added and subtracted to what value to obtain the CI range?

mean

How do we interpret Cohen's D of .61?

medium effect

Based on this information the researcher should make the decision to ___________.

reject the null hypothesis

If you fold a normal curve, each half would fit perfectly on top of the other. This characteristic is known as _______________.

symmetry

A type II error is made when

the null hypothesis is not rejected when it is false

The process of hypothesis testing starts with the assumption that

the null hypothesis is true