8/13/2019 Exam3_PracticeProblems

1/2

Psyc2300: Research Methods 1

Practice Problems

1. Imagine we transform all the scores in a sample into z-scores. What are the properties of thisstandardized distribution?

2. What is the difference between a standardized distribution and a distribution of samplingmeans?

3. Explain how sample size and the population standard deviation are related to the standard error ofthe mean.

4. Imagine Beth scored a 35 on a reading comprehension exam and a 543 on a memory test. We knowfrom previous testing that the mean reading comprehension for her grade level tends to be 38 (SD=

2.34). In addition, we know that for her age group the average memory score is 622 (SD= 44.12).Relative to her peers, on which test did Beth perform better?

5. We find that on a personality test of empathy, participants average a score of 48 (= 6.82). What isthe probability of obtaining a score of 52 and higher?

6. The scores on an introduction to psychology exam were 56, 42, 35, 62, 33, 42, and 31 from asample of students. Monica received the 56 on the exam. What is Monicas z-score?

7. We know that the average freshman watches 15.63 hours of TV per week (= 4.03) and that thedistribution tends to be normally distributed. We are conducting a study to determine the effect of

several types of advertising on freshmans buying habits. Before conducting the experiment, we

randomly sample 35 participants to find out whether or not participants in our part of the countryare similar to the national average. We find that our sample averages 17.53 hours of TV per week

(SD= 6.52). Is our sample a good representation of national average?

8. We know that college students tend to send an average of 16.55 text messages per day (= 3.53).After polling 83 students on KSUs campus, we find they send an average 14.92 text messages per

day (SD= 5.77). What is the probability of finding our sample mean of 14.92 or lower?

9. Imagine that our population, KSU college students, tend to work an average of 14.63 hours perweek (= 5.28) and that the distribution tends to be normal. What proportion of college students

tend to work between 18 and 20 hours per week?

10.We know that college students tend to send an average of 15.51 text messages per day (= 4.01).What is the minimum number of text messages sent by the top 20% of the distribution?

11.Researchers are interested a new drug that may reduce the symptoms of depression. However, theysuspect a possible side-effect could be changes in calorie intake, either a gain or a loss. Imagine

that in the general population it is known that middle-aged adults tend to consume an average of

2132 calories per day ( = 392). Additionally, image that the population is normally distributed.The researchers obtain a random sample of 49 participants and provide them with the drug. On

average, the sample consumes 2254 calories (SD= 302). Using a two-tailed test with a significant

level of = .05, answer the following questions.

a. State the null and alternative hypotheses.

8/13/2019 Exam3_PracticeProblems

2/2

Psyc2300: Research Methods 2

b. Draw a normal curve and indicate where the z-scores corresponding to the sample mean falland indicate where the critical region is located.

c. Indicate whether you would reject the null hypothesis or fail to reject the null. Explain yourdecision

12.Researchers are trying to determine if there is a correlation between the number of times studentsspeak in class and their scores on a 10 point quiz. Calculate the correlation for the data below:

Speaking (X) Quiz (Y)

2 6

0 5

5 9

1 8

Formulas that will be provided to you on the exam:

The following formulas will NOT be provided; however, you will still need to know them:Mean

Sum of squaresVariance

Standard deviation

Standard error of the mean

)1(

61

2

2

nn

D

X

sd

MX

n

YXXY

))(( yx SSSS

SP

M

M