STT 231 EXAM QUESTIONS AND
ANSWERS ALL CORRECT |2026
LATEST UPDATE
A study that aimed to assess whether traumatic events affect the proportion of female
births in a country reported data on the number of male and female births in Ireland in
June, 1997. That month, there were 2198 female and 2249 male births, which the
researchers used to compute a 95% confidence interval: (0.4796,0.5090). Although not
precisely true, assume throughout this question that the data from Ireland represent a
random sample of all births across the world in that month.
f this survey were replicated many times, each replication providing a 95% confidence
interval for the proportion of female births across the world in 1997, then 95% of the
resulting confidence intervals would be expected to capture the proportion of female
births across the world in June, 1997. - Answer- Correct
A package delivery service wants to compare the proportion of on-time deliveries for
two of its major service areas. In City A, 309 out of a random sample of 368 deliveries
were on time. A random sample of 262 deliveries in City B showed that202 were on
time.
Let 𝜋L = the "on time delivery rate for City A" and 𝜋 M = the "on time delivery rate for
City B". Which of the following is the correct set of hypotheses to test if the researchers
are interested in evaluating whether there is evidence that the delivery service rate is
different for City A and City B? - Answer- 𝑯𝟎 : 𝝅𝑨 − 𝝅𝑩 = 𝟎 vs. 𝑯𝒂 : 𝝅𝑨 − 𝝅𝑩 ≠ 𝟎
The test of the correct hypotheses from (a) yielded 𝑧 = 1.3578 with 𝑝 =0.1745 and ℎ7 =
0.1091. Which of the following conditions must be met for these results to be considered
statistically valid? Select all that apply.
_____ Condition 1: There must be an expected count of at least 5 for each level of the
categorical variable.
_____ Condition 2: The sample size must be at least 25 or the population data must be
normally distributed.
_____ Condition 3: There must be at least 10 "success" and 10 "failure"observations
expected across all 630 cases.
, _____ Condition 4: Each sampled data point must be independent of all other sampled
data points.
_____ Condition 5: There must be at least 10 "success" and 10 "failure"observations
expected in both samples - Answer- Condition 4 and 5
Using the same data, the researchers computed a 95% confidence intervalfor the true
difference in rates between City A and City B, (-0.0194, 0.1034).Use this information to
complete the sentence below:
If the researchers conducted a follow-up test of the hypotheses, 𝐻? : 𝜋Y − 𝜋 " =0.1 vs.
𝐻? : 𝜋Y − 𝜋 " ≠ 0.1, the p-value of this test would be _____ 0.05.
(Circleone)
greater than
less than
exactly - Answer- greater than
The test associated with the correct hypotheses in (a) yielded 𝑡 = 0.58876 with𝑝 =
0.2828 and 𝑑a = 0.2943. Use these findings in (b) to complete the following sentence:
Based on your results from (b), there is (circle one) - Answer- Little
The test associated with the correct hypotheses in (a) yielded 𝑡 = 0.58876 with𝑝 =
0.2828 and 𝑑a = 0.2943. Use these findings in (b) to complete the following sentence.
Our sample results indicate the estimated effect size is (circle one)
small. small to moderate. moderate to large. large. - Answer- Small to moderate
because < 2 is small and > 3 is moderate
The table below offers the results of three different follow-up studies. Which among
them most confirms (or replicates) the findings of the study results in (b)?Provide a 2-3
sentence justification of your choice that compares test statistics, p-values, and
estimated effect sizes across the studies. - Answer- Study B best replicates the findings
of the original study because its estimated effect size is similar (it's dramatically smaller
p-value reflects the fact that much more data was collected in Study B).
A study was conducted to identify the factors affecting quality of sleep for university
students. A survey of 290 students of different majors aged 17-29 years old revealed
that 67.2% of these students suffered from poor sleep.Further analyses were conducted
based off the original study of 290 university students in the question above. A second
study assessed if the distribution of sleep quality was the same for the various age
groups of Young (19 years old or younger), Middle (over19 but less than 24 years old),
and Old (24 years and older) university students. The following data shows the sleep
quality results for each group.a. Select the name of the test that should be used to
assess if the distribution of the responses is the same for the three age-group
populations
ANSWERS ALL CORRECT |2026
LATEST UPDATE
A study that aimed to assess whether traumatic events affect the proportion of female
births in a country reported data on the number of male and female births in Ireland in
June, 1997. That month, there were 2198 female and 2249 male births, which the
researchers used to compute a 95% confidence interval: (0.4796,0.5090). Although not
precisely true, assume throughout this question that the data from Ireland represent a
random sample of all births across the world in that month.
f this survey were replicated many times, each replication providing a 95% confidence
interval for the proportion of female births across the world in 1997, then 95% of the
resulting confidence intervals would be expected to capture the proportion of female
births across the world in June, 1997. - Answer- Correct
A package delivery service wants to compare the proportion of on-time deliveries for
two of its major service areas. In City A, 309 out of a random sample of 368 deliveries
were on time. A random sample of 262 deliveries in City B showed that202 were on
time.
Let 𝜋L = the "on time delivery rate for City A" and 𝜋 M = the "on time delivery rate for
City B". Which of the following is the correct set of hypotheses to test if the researchers
are interested in evaluating whether there is evidence that the delivery service rate is
different for City A and City B? - Answer- 𝑯𝟎 : 𝝅𝑨 − 𝝅𝑩 = 𝟎 vs. 𝑯𝒂 : 𝝅𝑨 − 𝝅𝑩 ≠ 𝟎
The test of the correct hypotheses from (a) yielded 𝑧 = 1.3578 with 𝑝 =0.1745 and ℎ7 =
0.1091. Which of the following conditions must be met for these results to be considered
statistically valid? Select all that apply.
_____ Condition 1: There must be an expected count of at least 5 for each level of the
categorical variable.
_____ Condition 2: The sample size must be at least 25 or the population data must be
normally distributed.
_____ Condition 3: There must be at least 10 "success" and 10 "failure"observations
expected across all 630 cases.
, _____ Condition 4: Each sampled data point must be independent of all other sampled
data points.
_____ Condition 5: There must be at least 10 "success" and 10 "failure"observations
expected in both samples - Answer- Condition 4 and 5
Using the same data, the researchers computed a 95% confidence intervalfor the true
difference in rates between City A and City B, (-0.0194, 0.1034).Use this information to
complete the sentence below:
If the researchers conducted a follow-up test of the hypotheses, 𝐻? : 𝜋Y − 𝜋 " =0.1 vs.
𝐻? : 𝜋Y − 𝜋 " ≠ 0.1, the p-value of this test would be _____ 0.05.
(Circleone)
greater than
less than
exactly - Answer- greater than
The test associated with the correct hypotheses in (a) yielded 𝑡 = 0.58876 with𝑝 =
0.2828 and 𝑑a = 0.2943. Use these findings in (b) to complete the following sentence:
Based on your results from (b), there is (circle one) - Answer- Little
The test associated with the correct hypotheses in (a) yielded 𝑡 = 0.58876 with𝑝 =
0.2828 and 𝑑a = 0.2943. Use these findings in (b) to complete the following sentence.
Our sample results indicate the estimated effect size is (circle one)
small. small to moderate. moderate to large. large. - Answer- Small to moderate
because < 2 is small and > 3 is moderate
The table below offers the results of three different follow-up studies. Which among
them most confirms (or replicates) the findings of the study results in (b)?Provide a 2-3
sentence justification of your choice that compares test statistics, p-values, and
estimated effect sizes across the studies. - Answer- Study B best replicates the findings
of the original study because its estimated effect size is similar (it's dramatically smaller
p-value reflects the fact that much more data was collected in Study B).
A study was conducted to identify the factors affecting quality of sleep for university
students. A survey of 290 students of different majors aged 17-29 years old revealed
that 67.2% of these students suffered from poor sleep.Further analyses were conducted
based off the original study of 290 university students in the question above. A second
study assessed if the distribution of sleep quality was the same for the various age
groups of Young (19 years old or younger), Middle (over19 but less than 24 years old),
and Old (24 years and older) university students. The following data shows the sleep
quality results for each group.a. Select the name of the test that should be used to
assess if the distribution of the responses is the same for the three age-group
populations
