STAT 121 Exam Questions Verified Answers
Latest Update 2025
T distribution is __________ and ___________ than a normal distribution
What happens to it when df increases? - ANS wider & shorter
gets closer to normal when df increases
What is margin of error? - ANS The amount we add and subtract from our sample statistic
to get our interval
How do you interpret a 90% confidence level? - ANS 90% of all the intervals we could obtain by
performing the same procedure over and over again would contain the parameter of interest.
How do you interpret a 95% confidence interval? - ANS We are 95% confident (or whatever
level) that the parameter (mean or proportion in context) is between this interval
When sample size changes, what happens to margin of error? - ANS As n increases, margin
of error decreases (more accurate)
When confidence level increases, how does margin of error increase? - ANS Margin of error
increases
How do you find sample size from margin of error? Do you round up or down? - ANS n = (z *
sigma/ m) ^2
Round UP to nearest whole number
Type 1 vs. Type 2 errors: How do you know what is what? - ANS ART is my BFF
Alpha Reject True H0
,Beta Fail to reject False H0
What is alpha & beta and power - ANS α - Probability of Rejecting a H0, when H0 is true
(probability of a Type I error)
β - Probability of a type II error (Failing to reject H0 when it is false)
Power = Probability of correctly rejecting H0 when H0 is false (1 - β)
The t statistic measures - ANS how many standard errors the observed x ̄is from the claimed
parameter value μ
Whenever performing a one sample t procedure on means, we should check for - ANS
randomization and no outliers in the data.
Sample results are said to be statistically significant whenever - ANS the difference between the
observed statistic and the claimed parameter value given in H0 is too large to be due to chance.
The margin of error in a confidence interval covers only which kind of errors? - ANS
chance errors due to random sampling
The purpose of a confidence interval is to provide - ANS plausible values that a parameter could
be.
The weekly oral dosage of anabolic steroids was measured on a sample of 20 body builders.
A 95% confidence interval estimate for the average weekly oral dose of anabolic steroids
obtained from these results was 152 mg to 194 mg. What is a correct interpretation of this
confidence interval? - ANS We are 95% confident that the average weekly dose of anabolic
steroids used by all body builders is between 152 mg. and 194 mg.
,The mean of the sample is 173 mg and the margin of error for the confidence interval given
in the above question is 21 mg. What is a correct interpretation of margin of error? - ANS The
maximum difference we expect between our sample result and the true average weekly oral
dose is no more than 21 mg.
Which of the following is a correct interpretation of 95% confidence? - ANS Using the same
procedure as was used to obtain the computed interval, we will obtain intervals that
contain the average weekly oral dose of anabolic steroids 95% of the time.
The value of a parameter will only change if
a) the population changes.
b) a different sample is obtained from the population.
c) the sample size is increased.
d) repeated samples are taken from the same population. - ANS a) the population changes.
What is the random variable of the sampling distribution of x?̄
a) the parameter being estimated
b) the response variable
c) the observations in the sample
d) the sample mean - ANS d) the sample mean
Which one of the following does NOT have variability?
a) a parameter
b) data
c) a statistic
d) a random variable
e) a quantitative response variable - ANS a) parameter
Which one of the following is NOT a parameter?
, a) the mean of the measurements on all the individuals in a population.
b) the proportion of a population that have a certain characteristic.
c) the standard deviation of an entire population.
d) the proportion in a sample survey that favor a certain opinion. - ANS d) the proportion in
a sample survey that favor a certain opinion
Fill in the blank: Central Limit Theorem allows us to compute probabilities on
___________ using the standard Normal table provided the sample size of the random
sample is sufficiently large.
a) x ̄
b) μ
c) s
d) sample measurements. - ANS a) x bar
The sampling distribution of a statistic has the following:
a) shape.
b) center.
c) spread.
d) all of the above. - ANS d) all of the above
Which one of the following measures the variability of a statistic?
a) the standard deviation of the data.
b) the standard deviation of the sampling distribution for the statistic.
c) the total sum of squared deviations of the observations about the mean.
d) the number of standard deviations that a statistic value differs from the parameter
value. - ANS b) the standard deviation of the sampling distribution for the statistic
Latest Update 2025
T distribution is __________ and ___________ than a normal distribution
What happens to it when df increases? - ANS wider & shorter
gets closer to normal when df increases
What is margin of error? - ANS The amount we add and subtract from our sample statistic
to get our interval
How do you interpret a 90% confidence level? - ANS 90% of all the intervals we could obtain by
performing the same procedure over and over again would contain the parameter of interest.
How do you interpret a 95% confidence interval? - ANS We are 95% confident (or whatever
level) that the parameter (mean or proportion in context) is between this interval
When sample size changes, what happens to margin of error? - ANS As n increases, margin
of error decreases (more accurate)
When confidence level increases, how does margin of error increase? - ANS Margin of error
increases
How do you find sample size from margin of error? Do you round up or down? - ANS n = (z *
sigma/ m) ^2
Round UP to nearest whole number
Type 1 vs. Type 2 errors: How do you know what is what? - ANS ART is my BFF
Alpha Reject True H0
,Beta Fail to reject False H0
What is alpha & beta and power - ANS α - Probability of Rejecting a H0, when H0 is true
(probability of a Type I error)
β - Probability of a type II error (Failing to reject H0 when it is false)
Power = Probability of correctly rejecting H0 when H0 is false (1 - β)
The t statistic measures - ANS how many standard errors the observed x ̄is from the claimed
parameter value μ
Whenever performing a one sample t procedure on means, we should check for - ANS
randomization and no outliers in the data.
Sample results are said to be statistically significant whenever - ANS the difference between the
observed statistic and the claimed parameter value given in H0 is too large to be due to chance.
The margin of error in a confidence interval covers only which kind of errors? - ANS
chance errors due to random sampling
The purpose of a confidence interval is to provide - ANS plausible values that a parameter could
be.
The weekly oral dosage of anabolic steroids was measured on a sample of 20 body builders.
A 95% confidence interval estimate for the average weekly oral dose of anabolic steroids
obtained from these results was 152 mg to 194 mg. What is a correct interpretation of this
confidence interval? - ANS We are 95% confident that the average weekly dose of anabolic
steroids used by all body builders is between 152 mg. and 194 mg.
,The mean of the sample is 173 mg and the margin of error for the confidence interval given
in the above question is 21 mg. What is a correct interpretation of margin of error? - ANS The
maximum difference we expect between our sample result and the true average weekly oral
dose is no more than 21 mg.
Which of the following is a correct interpretation of 95% confidence? - ANS Using the same
procedure as was used to obtain the computed interval, we will obtain intervals that
contain the average weekly oral dose of anabolic steroids 95% of the time.
The value of a parameter will only change if
a) the population changes.
b) a different sample is obtained from the population.
c) the sample size is increased.
d) repeated samples are taken from the same population. - ANS a) the population changes.
What is the random variable of the sampling distribution of x?̄
a) the parameter being estimated
b) the response variable
c) the observations in the sample
d) the sample mean - ANS d) the sample mean
Which one of the following does NOT have variability?
a) a parameter
b) data
c) a statistic
d) a random variable
e) a quantitative response variable - ANS a) parameter
Which one of the following is NOT a parameter?
, a) the mean of the measurements on all the individuals in a population.
b) the proportion of a population that have a certain characteristic.
c) the standard deviation of an entire population.
d) the proportion in a sample survey that favor a certain opinion. - ANS d) the proportion in
a sample survey that favor a certain opinion
Fill in the blank: Central Limit Theorem allows us to compute probabilities on
___________ using the standard Normal table provided the sample size of the random
sample is sufficiently large.
a) x ̄
b) μ
c) s
d) sample measurements. - ANS a) x bar
The sampling distribution of a statistic has the following:
a) shape.
b) center.
c) spread.
d) all of the above. - ANS d) all of the above
Which one of the following measures the variability of a statistic?
a) the standard deviation of the data.
b) the standard deviation of the sampling distribution for the statistic.
c) the total sum of squared deviations of the observations about the mean.
d) the number of standard deviations that a statistic value differs from the parameter
value. - ANS b) the standard deviation of the sampling distribution for the statistic
