Psy 10- HW questions
A researcher determines that students study an average of 80 minutes per week. Assuming these data are normally distributed, and the standard deviation is 20, what is the z score for students studying 60 min per week?
-1.0
A researcher records the number of bird calls made during an experimental session with robins. Assuming the data are normally distributed, N(7.2, 0.6), what is the probability that robins made more than nine bird calls during this experimental session? (Note. round z score to 2 decimal places.)
.0013
A therapist goes through her records and finds that 200 of her 400 patients showed significant improvement in mental health over the past year. Hence, the probability of her patients showing significant improvement in mental health is
0.50
A professor finds that the students' scores on the final exam follow a normal distribution, N(76, 8). On this exam, a score of 90 is an A. What is the z score for 90 (the cutoff for an A)?
1.75
A news poll showed that voters had no preference of either of three candidates. In this example, the probability of a vote, for say, Candidate A equals
1/3
In a sample of 20 participants, a researcher estimates the 95% CI for a sample with a mean of 5.4 and an estimated standard error of 1.6. What is the upper confidence limit for this interval?
8.8
A researcher conducts two t tests. Test 1 is a two-tailed test with a smaller size at a .05 level of significance. Test is a two-tailed test with a larger sample size at a .05 level of significance. What do you know about the degrees of freedom for each test?
Test 2 is associated with larger degrees of freedom
A sampling distribution of the sample mean is _____
a distribution of all sample means that could be obtained in samples of a given size from the same population
By definition, the probability of an outcome is _____ -the fraction of times an outcome is likely to occur -particularly useful for predicting the likelihood of random events -the proportion of times and outcome is likely to occur -all of these
all of these
In hypothesis testing, a researcher's decision ____
all of these -depends on the level of significance for a hypothesis test -can be retained or reject the null hypothesis -is based on probability theory
The first step to hypothesis testing requires that a researcher
state the hypothesis
_____ allows researchers to describe (1) how far mean scores have shifted in the population or (2) the percentage of variance that can be explained by a given variable
effect size
The normal distribution is symmetric, which means that___
scores above the mean are distributed the same as scores below the mean
The mean can take on any value and the standard deviation can take on any positive value. Therefore, ____
the are an infinite number of possible normal distributions
Which of the following statements regarding the null hypothesis is true?
the null hypothesis always makes statements about a population parameter
The unit of measurement distributed along the x-axis of a standard normal distribution is referred to as a ______.
z score
State the critical value(s) for a t test using a two-tailed test at a .05 level of significance: t(20)
+- 2.083
A researcher records the following response times (in seconds) to a visual stimulus. Assuming these data are normally distributed, N(23, 3.1), what is the probability that participants responded in 20 seconds or less? (Note. round z score to 2 decimal places.)
.1660
A researcher records the body mass index (BMI) scores for a group of participants. Participants who score between 25 and 30 on this scale are categorized as overweight. Assuming the data are normally distributed, N(28.4, 1.6), what percentage of participants fell in this overweight category? (Note. round z score to 2 decimal places.)
.8247
The standard normal distribution is normally distributed with a mean of ____ and a variance of ______.
0; 1
A researcher selects a sample of 121 participants from a population with a mean of 32 and a standard deviation of 22. What is the standard error of the mean?
2.0
A researcher selects a sample of 32 participants who are assigned to participate in a study with one group. What are the degrees of freedom for this test?
31
In a sample of 28 participants, a researcher estimates the 95% CI for a sample with a mean of 1.5 and an estimated standard error of 0.3. What is the confidence interval at this level of confidence?
95% CI (0.9, 2.1)
The mean crying time of infants during nap time at a local preschool is 12 mins. The school implements a new nap time routine in a sample of 25 infants and records an average crying time of 8 mins (SD=4.6). Test whether this new nap time routine reduced crying time at a .05 level of significance.
The new nap time routine significantly reduced crying time, t(24) = -4.35, p < .05.
A researcher believes that increasing attention given to children will improve mean academic performance. Therefore, the alternative hypothesis should be___
mean academic performance will increase
A researcher reports that the size of an effect in some population is d=0.88 Which of the following is an appropriate interpretation for d?
mean scores shifted 0.88 standard deviations in the population
Which of the following is NOT a characteristic of probability? -probability can never be negative -probability can be stated as a fraction or decimal -probability is most useful for describing fixed events -probability varies between 0 and 1
probability is most useful for describing fixed events
A researcher selects a sample of 36 students from a school population with a mean IQ of 100 and standard deviation of 12. She determines that the mean IQ in this sample is 104. Assuming she computes a z test at a .05 level of significance, what is the decision for a two-tailed test?
reject the null hypothesis; IQ scores in this sample are significantly higher than those in the population
What values are distributed along the x-axis for a sampling distribution of the sample mean? -scores -sample variances -both sample means and sample variances -sample means
sample means
The normal distribution has all of the following characteristics, except that -the total area under the curve is greater than 1.0 -its distribution is theoretical -it is symmetric -the mean, median, and mode are equal
the total area under the curve is greater than 1.0
A professor finds that the average SAT score among all students attending his college is 1150 (sigma= 150). He polls his class of 25 students and finds that the average SAT score is 1,200. Suppose he computes a z test at a .05 level of significance. What is his decision?
to reject the null hypothesis for an one-tailed test, but to retain the null hypothesis for a two-tailed test
A researcher obtains z= 2.04 for a z test. What is the decision for this test at a .05 level of significance?
to reject the null hypothesis, for either a one-tailed or a two-tailed test
The average response time to a bank robbery is about 9 mins. A local community wants to improve on this time, so they implement advanced training seminars. They find that the new response time for a sample of 36 police officers is 8 mins (SD = 4.2). Test whether this advanced training seminar reduced response time at a .05 level of significance.
This advanced training seminar did not reduce response time, t(35) = -1.43, p > .05.
The t distribution is similar to the z distribution except ___
all of these -it is associated with scores being more likely in the tails of the distribution -it is associated with greater variability -it is characterized by "thicker" tails compared with the z distribution
If the value of the test statistic is in the rejection region, then _____
all of these -the decision is to reject the null hypothesis -the absolute value of the test statistic is larger than the absolute critical value -p < alpha
A researcher selects a sample of 25 participants from a population with a mean of 10 and a standard deviation of 5. What is the probability of selecting a sample mean equal to at least 12?
equal to the probability of selecting a sample mean that is at most equal to 8
A researcher finds that the average preschool-aged child drinks two cups of milk per day. Assuming these data are normally distributed, the z score for the average cups per day in this example is ______.
exactly equal to 0
A method for testing a claim or hypothesis about a parameter in a population, using data measured in a sample, is called____
hypothesis testing
A researcher obtains z = 1.80 for a z test. What is the decision for this test at a .05 level of significance?
it depends on whether the test is one-tailed or two-tailed
A researcher selects a sample of 49 participants from a population with a mean of 12 and a standard deviation of 3.5. What is the probability of selecting a sample mean of 13 or larger from this population?
less than .03