Introductory Statistics Practice Exams FREE Sample Exam

Each student is assigned a number, and a computer generates 50 different random numbers to choose participants. Which sampling method is this?

Systematic sampling

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Convenience sampling

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Simple random sampling

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Cluster sampling

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A phone company wants to estimate how many of its customers are thinking of switching providers. It surveys customers who purchased a phone in the last 30 days and finds very few intending to switch. Why is the estimate likely too low?

Thirty days is too long a window for any survey

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Customers who buy phones cannot be surveyed about switching

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Recent buyers just committed to the company, so the frame systematically misses long-time and already-departed customers who are most likely to switch

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The estimate is too high, because new buyers always plan to switch

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A survey records each participant’s blood type as A, B, AB, or O. What is the level of measurement?

Ordinal

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Interval

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Nominal

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Ratio

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A company compares injury rates from past records for warehouse workers who chose to attend optional safety training versus those who did not. Why is a causal claim (‘training prevents injuries’) shaky here?

The study uses records, and records can never be used in statistics

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Injury rates are categorical, so no comparison is possible

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It is an observational study: workers who choose training may already be more safety-conscious, a confounder that records alone cannot remove

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The workers were randomly assigned by their job titles

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A mail survey gets replies from only 30% of those contacted, and those who reply tend to be older than those who do not. The main problem is:

Undercoverage of young people in the frame

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Nonresponse bias, because nonrespondents differ systematically from respondents

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A leading question

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Random sampling error only

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A study measures weekly television hours and blood cholesterol for 500 adults and finds higher TV hours go with higher cholesterol. A critic says the study ‘ignored diet and exercise.’ In technical terms, the critic is pointing to:

A margin of error that is too large

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Lurking (confounding) variables that are associated with both TV hours and cholesterol

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A placebo effect in the cholesterol measurements

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Random assignment that was done poorly

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What is the defining feature of an observational study?

Researchers assign treatments at random

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Researchers use a placebo

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Researchers observe and record variables without imposing a treatment

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Researchers control every variable

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Distributions P and Q both have median 100. P has IQR 10 and Q has IQR 40. In which distribution would a value of 130 be more remarkable, and why?

In P: 130 lies far outside P's tightly packed middle 50%, while Q's middle values already spread widely

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In Q: a larger IQR makes every value more unusual

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Equally remarkable: the medians are the same

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In neither: 130 exceeds the median, so it is an outlier in both

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Find the five-number summary of: 4, 6, 8, 10, 12, 14, 16, 18, 20, 22.

Min 4, Q1 8, median 13, Q3 18, max 22

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Min 4, Q1 10, median 12, Q3 16, max 22

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Min 4, Q1 8, median 12, Q3 18, max 22

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Min 6, Q1 8, median 13, Q3 18, max 20

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A data set has IQR = 14 and Q3 = 70. Which of these values would NOT be flagged as a high outlier?

88: the upper fence is 70 + 1.5(14) = 91, and 88 is inside it

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92: it barely exceeds Q3 plus the IQR

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95: large values are always acceptable

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100: it is a round number

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A data set of package weights has a standard deviation of exactly 0. What must be true of the packages?

The packages have no weight

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All the packages have exactly the same weight

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Half the packages are above and half below the mean weight

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The weights are perfectly normally distributed

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Let X be uniform on 2 to 8. What is P(3 < X < 5)?

0.20

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About 0.33

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0.50

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About 0.67

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Introductory Statistics Practice Exams FREE Sample Exam — Fixed Set

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