
Concept explainers
Scores from a questionnaire measuring social anxiety form a
- a. for a random sample of n = 4 people?
- b. for a random sample of n = 16 people?
- c. for a random sample of n = 25 people?
a.

Answer to Problem 11P
The probability of obtaining a sample mean greater than M=53 for given sample is 0.2743.
Explanation of Solution
Given info:
Numbers of people in a random sample are n=4.
Population mean is μ=50.
Population standard deviation is σ=10.
Sample mean is M=53.
Calculation:
If μ and σ represents the population mean and standard deviation respectively. Let n represents numbers of scores in each sample. Let M represents given sample mean. Then,
μ=50σ=10n=4M=53
Let ˉX represents the random sample mean from given distribution. Let μM and σM represents mean and standard error of ˉX Then, expected mean of ˉX will be same as population mean and standard error is calculated as:
μM=50σM=σ√n=10√4=5
Let p represents the probability that random mean is greater than M=53.
p=P(ˉX>53)=1−P(ˉX<53)
Software procedure:
Step-by-step procedure to obtain the P(ˉX<53) using the SPSS software:
- Click on first empty block of data view.
- Go to Transform>Choose Compute variable>Enter Probability in Target Variable.
- Choose CDF& Noncentral CDF under Function group> choose CDF.Normal> drag it to the numeric expression.
- Enter 53,50,5 in the braces of CDF.NORMAL
- Choose OK.
Output using the SPSS software is given below:
From the SPSS output, P(ˉX<53) is 0.7257.
Using (1) p is calculated as:
p=1−P(ˉX<53)=1−0.7257=0.2743
Thus, the probability of obtaining a mean greater than M=53 for given sample is 0.2743.
b.

Answer to Problem 11P
The probability of obtaining a sample mean greater than M=53 for given sample is 0.1151.
Explanation of Solution
Given info:
Numbers of people in a random sample are n=16.
Population mean is μ=50.
Population standard deviation is σ=10.
Sample mean is M=53.
Calculation:
If μ and σ represents the population mean and standard deviation respectively. Let n represents numbers of scores in each sample. Let M represents given sample mean. Then,
μ=50σ=10n=16M=53
Let ˉX represents the random sample mean from given distribution. Let μM and σM represents mean and standard error of ˉX Then, expected mean of ˉX will be same as population mean and standard error is calculated as:
μM=50σM=σ√n=10√16=2.5
Let p represents the probability that random mean is greater than M=53.
p=P(ˉX>53)=1−P(ˉX<53)
Software procedure:
Step-by-step procedure to obtain the P(ˉX<53) using the SPSS software:
- Click on first empty block of data view.
- Go to Transform>Choose Compute variable>Enter Probability in Target Variable.
- Choose CDF& Noncentral CDF under Function group> choose CDF.Normal> drag it to the numeric expression.
- Enter 53,50,2.5 in the braces of CDF.NORMAL
- Choose OK.
Output using the SPSS software is given below:
From the SPSS output, P(ˉX<53) is 0.8849.
Thus,
p=1−P(ˉX<53)=1−0.8849=0.1151
Hence, the probability of obtaining a mean greater than M=53 for given sample is 0.1151.
c.

Answer to Problem 11P
The probability of obtaining a sample mean greater than M=53 for given sample is 0.0668.
Explanation of Solution
Given info:
Numbers of people in a random sample are n=25.
Population mean is μ=50.
Population standard deviation is σ=10.
Sample mean is M=53.
Calculation:
If μ and σ represents the population mean and standard deviation respectively. Let n represents numbers of scores in each sample. Let M represents given sample mean. Then,
μ=50σ=10n=25M=53
Let ˉX represents the random sample mean from given distribution. Let μM and σM represents mean and standard error of ˉX Then, expected mean of ˉX will be same as population mean and standard error is calculated as:
μM=50σM=σ√n=10√25=2
Let p represents the probability that random mean is greater than M=53.
p=P(ˉX>53)=1−P(ˉX<53)
Software procedure:
Step-by-step procedure to obtain the P(ˉX<53) using the SPSS software:
- Click on first empty block of data view.
- Go to Transform>Choose Compute variable>Enter Probability in Target Variable.
- Choose CDF& Noncentral CDF under Function group> choose CDF.Normal> drag it to the numeric expression.
- Enter 53,50,2 in the braces of CDF.NORMAL
- Choose OK.
Output using the SPSS software is given below:
From the SPSS output, P(ˉX<53) is 0.9332.
Thus,
p=1−P(ˉX<53)=1−0.9332=0.0668
Hence, the probability of obtaining a mean greater than M=53 for given sample is 0.0668.
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Chapter 7 Solutions
Essentials of Statistics for The Behavioral Sciences (MindTap Course List)
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