STA 210 Final

the correlation coefficient is always:

between -1 and 1

in class we relegated all confounding to two possible sources. what were those?

improper comparison and lack of randomization

HA always implies what?

statistical significance

Recall the online learning study you read about in BN 1.14. What was one obvious source of confounding that threatens the article's conclusion that online learning is no less effective than face-to-face learning?

students got to self-select; that is to decide for themselves which course (online or face-to-face) they enrolled in.

If someone reports that a hypothesis has been tested with an assumed Type I error rate of 0.05 and the results failed to be statistically significant, then we can say that

the p-value for this application is > 0.05

what do we mean by statistical significance

treatment differences that are sufficiently large that you say they re unlikely to have happened by chance

which of the following is a strategy for reducing non-sampling errors?

use of incentives for non-responders

If we are testing the hypothesis H0: p ≤ 0.35 versus HA: p > 0.35 and we compute z to be 0.5, then what can you say? A copy of the Standard Score Table is attachedPreview the document.

we fail to have convincing evidence that p is > 0.35

in our class what do we mean when we say the results of a certain test are "not statistically significant?"

we mean we have not been able to reject the HO with a Type I error rate that is tolerable (usually 0.05)

If you know that 38% of all sample proportions will fall within 0.5 standard deviations from the parameter p, what is the formula for a 38% margin of error?

(1/4)x(1/sqrt(n))

In a study reported in the Chicago tribune, in 2012, twenty-four students were fatally shot during the school year that ended June 15, four fewer than in the 2010-11 year. But the overall shooting toll —319—was the highest in four years and a nearly 22 percent increase from 2011. What was the total number of shootings in 2011?

261

Let's assume you have developed a model designed to screen for the stability of banks and predict bankruptcy. So your model is designed to "sound an alarm" if it predicts a bank will become bankrupt (a "positive"). To test how well you model is working, it was applied to 3000 banks, 286 of which were known to have gone bankrupt and 2714 of which remained solvent. The data collected from the study are in the 2x2 table below. Please answer the following questions in the spaces provided. What is the specificity of your model?

2689/2714

if the standard deviation of a set of data is computed to be 4, then the variance is:

4

A precinct has 21,441 registered voters, 49 percent Democrat, 51 percent Republican. An SRS of 100 (yielding 72 Democrats and 28 Republicans) are asked: "Do you support a path to citizenship for DACA recipients?" 50% of the Republicans (14) say "yes" and 75% of the Democrats (54) say "yes." If the estimated of all registered voters in this precinct who would say "yes" to this question is reweighted to reflect the distribution of Republicans and Democrats in the precinct population, what would it be in this case (approximately)?

62%

Look at the sampling distribution plot shown below. This is the sampling distribution of the sample proportion. What is the standard deviation of the sampling distribution of the sample proportion based on a sample of size 500?

0.022

A sample of n = 20 U.K. students is taken and each one is asked "Does knowing that many of the basketball players U.K. recruits will go pro after one year affect your sense of attachment to the team?" Suppose 55% in your sample said "yes, it does affect my attachment." You want to know if it is safe for the Kernel to report that a majority of all U.K. students are likely to feel that way. So your job is to decide between H0: p ≤ 0.50 and HA: p > 0.50, where p is the true proportion of all UK students who would have said "yes" had all been asked. What is the p-value (more or less) associated with this decision? A Standard Score Table is attachedPreview the document.

0.33

Suppose you are testing H0: p = p0 vs. HA: p ≠ p0. If you get a standard score (z value) of 0.87, what is the corresponding p-value for this test? A Standard Score Table is attachedPreview the document.

0.38

We worked a fair amount with data from the NHTSA's 1998 San Diego field sobriety test validation study, issued by the agency as the report "Validation of the Standardized Field Sobriety Test Battery at BACs Below 0.10 Percent," by Drs. Jack Stuster and Marcelline Burns. A copy of part of this data set is attachedPreview the document. Assume a BAC of 0.04 or above means you are (in reality) drunk. Twenty-nine participants were legally sober according to the BACs, while 267 had BACs greater than or equal to 0.04 and were, hence, legally drunk. If you were to take as your test that a Total FST (that is, the sum of the scores on HGN, OLS, WAT) of 5 or more means you are drunk then what would be the false positive rate?

0.48

Let A = Ottawa Ankle Test Says Ankle is Broken; and B = Ankle Really is Broken. Suppose you know the following. P(A|B) = .8; P(A) = .4; P(B) = .3. What is P(B|A)? Use Bayes Rule.

0.60

The CEO of a large electric utility claims that more than 80 percent of his customers are very satisfied with the service they receive. To test this claim, the local newspaper surveyed 1000 customers, using simple random sampling. Among the sampled customers, 81% say they are very satisfied. We want to decide if the 81% is enough evidence to lead us accept or reject the CEO's claim. What is the standard score associated with a test of the hypothesis H0: p ≤ 0.80 vs HA p > 0.80?

0.79

We worked a fair amount with data from the NHTSA's 1998 San Diego field sobriety test validation study, issued by the agency as the report "Validation of the Standardized Field Sobriety Test Battery at BACs Below 0.10 Percent," by Drs. Jack Stuster and Marcelline Burns. A copy of part of this data set is attachedPreview the document. Assume a BAC of 0.04 or above means you are (in reality) drunk. Twenty-nine participants were legally sober according to the BACs, while 267 had BACs greater than or equal to 0.04 and were, hence, legally drunk. If you were to take as your test that a Total FST (that is, the sum of the scores on HGN, OLS, WAT) of 5 or more means you are drunk then what would the sensitivity be?

0.91

On June 2, 2007, a nurse in Wales accidentally injected an 85-year-old patient with a lethal amount of insulin during a home visit. The syringes used to inject insulin are typically marked with insulin units instead of the usual milliliters. Finding herself without an insulin syringe on hand, the nurse retrieved a new syringe from her car. She did not notice, however, that the syringe she grabbed was marked in milliliters instead of insulin units. If 1 milliliter equals 100 insulin units, how many milliliters should the patient have been given if she had been prescribed 36 units?

1 milliliter = 100 units so 0.01 milliliter = 1 unit. it follows that 0.36 milliliters = 36 units. so she should have injected the patient with 0.36 milliliters.

Please read the following article from CBS News. What is the sample for the CBS News Poll? Title: Poll: Majority of Americans Back Stricter Gun Laws Authors: Sarah Dutton, Jennifer De Pinto, Anthony Salvanto, Fred Backus and Leigh Ann Caldwell Source: CBS News January 17, 2013 As the president outlined sweeping new proposals aimed to reduce gun violence, a new CBS News/ New York Times poll found that Americans back the central components of the president's proposals, including background checks, a national gun sale database, limits on high capacity magazines and a ban on semi-automatic weapons. Asked if they generally back stricter gun laws, more than half of respondents—54%—support stricter gun laws ... That is a jump from April—before the Newtown and Aurora shootings—when only 39% backed stricter gun laws but about the same as ten years ago. ... This poll was conducted by telephone from January 11-15, 2013 among 1,110 adults nationwide. Phone numbers were dialed from samples of both standard land-line and cell phones. The error due to sampling for results based on the entire sample could be plus or minus three percentage points.

1,110 adults contacted by phone

In the context of screening tests, specificity is the same as:

1-the false positive rate.

What sample size would you have to take if you wanted a 99.9% margin of error of ½ of 1 percent?

108,241

In BN 2.29 you studied about the role of incentives and whether they mattered. Table 2.10 (shown below) recorded the results of the Early Response incentive. What two numbers or percentages would you use to evaluate the effect of "Incentive" versus "No Incentive" on Early Response?

16% and 32%

A precinct has 21,441 registered voters, 49 percent Democrat, 51 percent Republican. An SRS of 100 (yielding 72 Democrats and 28 Republicans) are asked: "Do you support a path to citizenship for DACA recipients?" 50% of the Republicans (14) say "yes" and 75% of the Democrats (54) say "yes." What is the sample proportion who answered "yes" to this question (approximately)?

68%

A (real) test was constructed as a way of checking to see if Retinal Vein Pulsation (RVP) was reliable as a test for Intracranial Pressure (IP). The absence of RVP is considered to be indicative of dangerous IP. So the test looks for absence of RVP and in that sense "absence" is a "positive" outcome. A study enrolled 189 patients and each patient was given this RVP test. Results of the testing, along with a categorization of High or Normal IP is in the table. What is the positive predictive value of this test?

70%

The distribution shown here represents the sampling distribution that resulted from 44 simple random samples, each of size 50, taken from a manufactured population of 250 people. In each case the proportion of sampled individuals who agreed that Facebook was doing an adequate job protecting users' data was recorded. About what percentage of the time did a sample percentage between 21% and 36% occur?

80%

A (real) test was constructed as a way of checking to see if Retinal Vein Pulsation (RVP) was reliable as a test for Intracranial Pressure (IP). The absence of RVP is considered to be indicative of dangerous IP. So the test looks for absence of RVP and in that sense "absence" is a "positive" outcome. A study enrolled 189 patients and each patient was given this RVP test. Results of the testing, along with a categorization of High or Normal IP is in the table. What is the specificity of this test?

88%

Please read the following article from CBS News. This survey reports a margin of sampling error of about 3%. Using the formulas for MOE you learned in this class, what level of confidence does this MOE seem to correspond to? Title: Poll: Majority of Americans Back Stricter Gun Laws Authors: Sarah Dutton, Jennifer De Pinto, Anthony Salvanto, Fred Backus and Leigh Ann Caldwell Source: CBS News January 17, 2013 As the president outlined sweeping new proposals aimed to reduce gun violence, a new CBS News/ New York Times poll found that Americans back the central components of the president's proposals, including background checks, a national gun sale database, limits on high capacity magazines and a ban on semi-automatic weapons. Asked if they generally back stricter gun laws, more than half of respondents—54%—support stricter gun laws ... That is a jump from April—before the Newtown and Aurora shootings—when only 39% backed stricter gun laws but about the same as ten years ago. ... This poll was conducted by telephone from January 11-15, 2013 among 1,110 adults nationwide. Phone numbers were dialed from samples of both standard land-line and cell phones. The error due to sampling for results based on the entire sample could be plus or minus three percentage points.

95%

The average score on a marketing professor's first exam in his sports marketing class is a 70 with a standard deviation of 6. Assuming the distribution of scores is bell-shaped, what percentage of students scored between 58 and 82?

95%

In Excel what is the function for finding the correlation coefficient? Google on this if you don't know.

=CORREL( )

What is a quasi-experiment?

Experiments unable to use randomization to evaluate treatment effectiveness.

Please read the article here on the libido drug Flibanserin. Was the alternative accepted or not? How do you know? From Time Health Women in the flibanserin group self-reported an average of 2.8 sexually satisfying events in the four-week baseline period. In the final four weeks of the 24-week study period, those women reported an average of 4.5 sexually satisfying events, a more than 50% increase. Women in the placebo group reported an average increase from 2.7 events to 3.7. The difference in effect between flibanserin and the placebo— about 0.8 sexually satisfying events—was statistically significant, the drug company said. The side effects from the drug, which included dizziness and fatigue, among others, were mild to moderate and transient.

HA was accepted, because the results were statistically significant

Read the following excerpt from the Washington Post. The words "statistically significant" are used. Assuming Mr. Wolf is using those words correctly, what seems to have been chosen during his study, an H0 or an HA? Title: White House Ignores Evidence of How D.C. School Vouchers Work Author: Editorial Board Opinion Source: Washington Post, March 29, 2011 Consider the following statements from a recent Washington Post editorial discussing the Obama strongly worded dismissal of school vouchers. The article says: That dismissal might come as a surprise to Patrick J. Wolf, the principal investigator who helped conduct the rigorous studies of the D.C. Opportunity Scholarship Program and who has more than a decade of experience evaluating school choice programs. Here's what Mr. Wolf had to say about the program in Feb. 16 testimony to the Senate Committee on Homeland Security and Governmental Operations. "In my opinion, by demonstrating statistically significant experimental impacts on boosting high school graduation rates ... the DC OSP has accomplished what few educational interventions can claim: It markedly improved important education outcomes for low-income inner-city students."

HA, since that is always what statistical significance implies

Read the following article on pagoclone. What H0 and HA are being tested? Drugs for Stutterers Title: Drug for Stutterers Shows Promise: Indevus Says Pill Reduced Incidents for Most in 1st Trial Author: Stephen Heuser Source: Boston Globe, May 25, 2006 The following is an extract from a Boston Globe article on stuttering: A potential pill to treat stuttering took a step forward yesterday when Indevus Pharmaceuticals Inc. of Lexington said its experimental drug reduced stuttering in a majority of patients in its first clinical trial. The 132-patient trial is the largest human test ever conducted on a drug for stuttering, according to the company. ... The Indevus drug, called pagoclone, was given to 88 patients in escalating doses, with the rest of the trial subjects receiving a placebo. The patients were then tracked using several widely accepted measures of stuttering. On a third rating scale, based on doctors' impressions, the pagoclone patients scored a "numerically superior rating" to the placebo group, but the finding did not reach statistical significance.

HO: pagoclone is no different than placebo vs. HA: pagoclone is better than a placebo.

Read the article given here on the effects of pumpkin seed oil on urinary issues in men. Clearly identify what the null (H0) and alternative (HA) appear to be in the context of this article. Pumpkins and Prostate Health Title: Pumpkin Seed Oil May Be a Halloween Treat Author: Elena Conis Source: Los Angeles Times, October 25, 2010 In the News ... According to the article in the Los Angeles Times by Elena Conis, for centuries pumpkin seeds have been a home remedy used to control or increase the frequency of urination in adults, children, and livestock. Knowing this about pumpkin seeds has prompted researchers to explore the possibility of a link between eating the seeds and better prostate health. German researchers have been very involved in exploring this possible connection. The article summarized one study, the results of which were published in a German journal in 2000. According to the Los Angeles Times, the study: randomly selected among about 500 men to take either 1,000 milligrams of pumpkin seed oil extract or a placebo every day for 12 months. Symptoms improved in 65% of the men who took the oil, which the researchers interpreted as a promising (and statistically significant) result, even though symptoms also improved in 54% of the men who took the placebo.

HO: pumpkin seed oil no better treating urinary issues than a placebo vs. HA: pumpkin seed oil is better treating urinary issues than a placebo

Read the following excerpt from the Washington Post. The words "statistically significant" are used. What H0 and HA are being tested? Title: White House Ignores Evidence of How D.C. School Vouchers Work Author: Editorial Board Opinion Source: Washington Post, March 29, 2011 Consider the following statements from a recent Washington Post editorial discussing the Obama strongly worded dismissal of school vouchers. The article says: That dismissal might come as a surprise to Patrick J. Wolf, the principal investigator who helped conduct the rigorous studies of the D.C. Opportunity Scholarship Program and who has more than a decade of experience evaluating school choice programs. Here's what Mr. Wolf had to say about the program in Feb. 16 testimony to the Senate Committee on Homeland Security and Governmental Operations. "In my opinion, by demonstrating statistically significant experimental impacts on boosting high school graduation rates ... the DC OSP has accomplished what few educational interventions can claim: It markedly improved important education outcomes for low-income inner-city students."

HO: vouchers don't help graduation rates vs. HA yes, they do.

two variables measured on the same individual are associated if:

If some values of one of the variables tend to occur more often with certain values of the second variable than with other values of that variable

A plot very similar to the one shown here was allegedly presented to the Kentucky House of Representatives as part of an overall message that an increase in CO2 emissions causes a decrease in child mortality rates. What would you say in response to this argument?

It's irrational; the pairing of high C02 emissions with low mortality rates only shows an association. There is no evidence of direct cause and effect.

Suppose A = "condition is really present," B = "test says condition is present," C = "condition is really not present, " and D = "test says condition is not present." In symbols, what is analogous to specificity?

P(D|C)

A plot very similar to the one shown here was allegedly presented to the Kentucky House of Representatives as part of an overall message that related CO2 emissions to child mortality. How did taking log base 10 of each variable shown, and making a new plot, make using "r" more reasonable for measuring association?

The transformed scatterplot went from showing a curved trend to showing a straight line trend.

Suppose we have data like in Problem 4 that can be into a so-called 2x2 table like you see below. The letters U, V, W, X just stand for the counts that are in those cells. What is the probability of getting a Grade of C or Better if you ate breakfast, divided by the probability of getting a Grade Below C if you ate breakfast?

U/V

What is a Type II error most analogous to?

a false negative

In September of 2016, an article in The Denver Post declared "Colorado in Dead Heat Between Hillary Clinton and Donald Trump." The article went on to say: "The survey by CNN and ORC International found 42 percent of likely Colorado voters backed Trump compared to the 41 percent who supported Clinton; a statistical tie given the margin of error of 3.5 percentage points." The article did not report the sample size. However, if this margin of error is a 95% margin of error, what would the sample size have to be, more or less? (You might find the following generic confidence interval information useful:)

about 816

Please read the following article from CBS News. What is the population for the CBS News Poll? Title: Poll: Majority of Americans Back Stricter Gun Laws Authors: Sarah Dutton, Jennifer De Pinto, Anthony Salvanto, Fred Backus and Leigh Ann Caldwell Source: CBS News January 17, 2013 As the president outlined sweeping new proposals aimed to reduce gun violence, a new CBS News/ New York Times poll found that Americans back the central components of the president's proposals, including background checks, a national gun sale database, limits on high capacity magazines and a ban on semi-automatic weapons. Asked if they generally back stricter gun laws, more than half of respondents—54%—support stricter gun laws ... That is a jump from April—before the Newtown and Aurora shootings—when only 39% backed stricter gun laws but about the same as ten years ago. ... This poll was conducted by telephone from January 11-15, 2013 among 1,110 adults nationwide. Phone numbers were dialed from samples of both standard land-line and cell phones. The error due to sampling for results based on the entire sample could be plus or minus three percentage points.

all adult Americans

A Dean of Admissions at U.K. once tallied up the ACT scores for ALL entering freshman for that year and reported that the average was 25. He then attached a margin of error at the urging of a faculty member in the audience. That faculty member was:

confused, because the Dean's figure was not subject to any sampling variability

A Ph.D. candidate in the College of Education once defended her misleading and confusing questionnaire by arguing that her margin of error was low, only about 3%. This argument is:

confused, because the margin of error has nothing to do with poor questionnaire designs

We looked at a study that showed college students who ate breakfast had a higher success rate on General Biology exams than those students who did not eat breakfast. The operative graph is repeated below. What does the graph tell you?

eating breakfast is associated with better class performance

A survey was conducted by Playboy, asking questions about the sex lives of 5,000 U.S. University and College students. One question asked: "Are you in a nude picture on someone's camera phone?" 34 percent said "yes". Name at least one error you'd expect this survey to suffer from even if all 15.9 million College and University students in the U.S. had answered, and not just 5,000.

error caused by fabricated responses

You plan to take a sample of 200 voters in Kentucky and ask "Do you think former Cambridge Analytica employee Chris Wylie should be considered a hero?" You take your sample and have a sample proportion of 75% who say they think Snowden should be considered a hero. If you are choosing between HO: p < 0.73 (line under it) HA: p > 0.73 what decision do you make and why? Take α = 0.05. Use the Standard Score Table that is attachedPreview the document.

hair to reject HO with a p-value bigger than 0.05

Recall the article about the Harris Poll that was discussed in one of our BN assignments. Harris is a major polling organization that refuses to accompany their poll reports with a margin of error. What is one reason that was given for such a bold omission?

harris recognized that there are many sources of error that are not addressed by the MOE, so reporting it might be misleading

Why did Subway stop using azodicarbonamide in its breads?

it (or its breakdown products) was found to cause cancers of the lung and blood vessels in mice

We worked a fair amount with data from the NHTSA's 1998 San Diego field sobriety test validation study, issued by the agency as the report "Validation of the Standardized Field Sobriety Test Battery at BACs Below 0.10 Percent," by Drs. Jack Stuster and Marcelline Burns. Assume a BAC of 0.04 or above means you are (in reality) drunk. Twenty-nine participants were legally sober according to the BACs, while 267 had BACs greater than or equal to 0.04 and were, hence, legally drunk. Suppose you changed your rule to require that the Total FST score needed to say you were drunk was 2 or above instead of 5 or above. What will happen to your false negative rate?

it decreases

What can one say about the sampling distribution of a sample statistic based on a simple random sample?

it is about bell-shaped and peaked over the parameter

Please read the following article on antivirus software. What does the article mean by detection rate? Title: False Positives Sink Antivirus Ratings Author: By Neil J. Rubenking Source: PC Reviews, April 15, 2015 It's not enough for your antivirus to wipe out malicious software. It also has to leave legitimate applications alone. In a recent test, quite a few products showed weakness in the latter area. A product that demonstrates adequate antivirus protection receives certification at the Standard level. Products that go above and beyond can earn Advanced or Advanced+ certification. If a product doesn't even achieve Standard certification, the report lists it as simply Tested. Based solely on detection rates, 13 products would have rated Advanced+ and six would have earned Advanced. Just one (Trend Micro) would have come in at the basic Standard level, and one (Microsoft) as Tested. However, false positives dragged down the score for a dozen of the tested products

it is like "sensitivity" - the ability to identify a positive (virus) correctly.

A plot very similar to the one shown here was allegedly presented to the Kentucky House of Representatives as part of an overall message that CO2 emissions are negatively associated with child mortality rates. What would you say in response to this argument?

it is reasonable, low CO2 emissions are somewhat paired with high mortality rates.

What is the "negative predictive value" of a screening test?

it is the probability the condition is really absent, given the test came back negative.

We used the concepts of sensitivity and specificity to create a transition from concepts that were familiar, to formal hypothesis testing, which was less familiar. In this transition we chose to view a hypothesis as a screening test. In that context of testing H0 versus HA, what does it mean to have a "false positive"?

it means you would conclude HA is true when really HO is.

What does MOE stand for?

margin of error

The following graph is from the Florida Department of Law Enforcement. It has been used to argue that murder decreased in Florida once a 2005 "Stand Your Ground" law was enacted. Does the graph actually support that statement?

no. the y-axis is inverted so the dip after 2005 is actually a spike.

what do we mean by "human inference?"

off-hand phrase taken to mean inference we make from statistical constructs

The claim has been made that over 4 million women in the U.S. are battered to death each year by a spouse or boyfriend. What is wrong with this claim?

only about 2.4 million people died in the U.S each year from all causes

what is the legal analogy to a null hypothesis

presumption of innocence

A survey was conducted by Playboy, asking questions about the sex lives of 5,000 U.S. University and College students. One question asked: "Are you in a nude picture on someone's camera phone?" 34 percent said "yes". Other samples of size 5,000, if asked the same question, would likely not produce a sample percentage of 34%. What is this variability called?

sampling variability

What is the Delaney Clause?

says that if a substance causes cancer in animals then it can't be considered safe for use in food products

If you compute a correlation coefficient to be -0.26 what does that tell you about the scatterplot, all things being equal?

should be a recognizable, though not strong, downward to the right trend

Read the following excerpt from the Washington Post. What does the decision that was made claiming that vouchers boost graduation rates have to do with a kind of false positive rate? Title: White House Ignores Evidence of How D.C. School Vouchers Work Author: Editorial Board Opinion Source: Washington Post, March 29, 2011 Consider the following statements from a recent Washington Post editorial discussing the Obama strongly worded dismissal of school vouchers. The article says: That dismissal might come as a surprise to Patrick J. Wolf, the principal investigator who helped conduct the rigorous studies of the D.C. Opportunity Scholarship Program and who has more than a decade of experience evaluating school choice programs. Here's what Mr. Wolf had to say about the program in Feb. 16 testimony to the Senate Committee on Homeland Security and Governmental Operations. "In my opinion, by demonstrating statistically significant experimental impacts on boosting high school graduation rates ... the DC OSP has accomplished what few educational interventions can claim: It markedly improved important education outcomes for low-income inner-city students."

the FPR is essentially the same as an assumed Type I error rate, typically taken to be 0.05. in this case, the p-value must have been smaller than 0.05

In the context of hypothesis testing, good sensitivity speaks to:

the ability of the test to reject a false HO.

Suppose you are testing the null hypothesis H0: p ≤ 0.75 versus HA: p > 0.75 and compute a standard score z to be = 2.18. What decision do you make and why? A Standard Score Table is attachedPreview the document.

the associated p-value is about the 0.015. this is smaller than a Type I error rate of 0.05, so we accept HA.

Read the article by Dr. Justin Lehmiller, below.This difference in distance they refer to was said to be "statistically significant" in a follow up to this article. What does the author say about practical significance in this study? In the article "DOES OXYTOCIN HELP MEN STAY FAITHFUL TO THEIR WIVES?" (November 19th, 2012), by Dr. Justin J. Lehmiller, we read (paraphrased): In a new study published in The Journal of Neuroscience, 86 heterosexual men either received three puffs of a nasal spray containing oxytocin or a placebo solution. Approximately half of the men were currently involved in a monogamous romantic relationship and the other half were single. Forty-five minutes after receiving the spray, participants were asked to ... interact with an attractive female research assistant in person. As part of this interaction, subjects had to choose the ideal distance to stand from her. (Partnered) men who received the placebo maintained a distance of approximately 21-24 inches. Partnered guys (on the oxytocin treatment) stayed an average of 27 to 31 inches (68-79 cm) away. So oxytocin therefore prevents cheating, right? Not exactly. First, there was no actual measure of infidelity or even temptation to cheat. We're just assuming that how far they stood (is a proxy) for temptation. To demonstrate that oxytocin actually reduces cheating, we would need a long-term clinical trial in which guys in relationships are given oxytocin or a placebo and then we would see who reports cheating more over a specified period of time. Second, is keeping an extra 6 or 7 inches away from someone who is really hot actually going to ensure fidelity? It's not like the guys who got oxytocin ran away screaming—they just stood back an extra couple of inches.

the author doubts that six or seven inches difference is any real evidence of fidelity.

We looked at a study that showed college students who ate breakfast had a higher success rate on General Biology exams than those students who did not eat breakfast. The operative graph is repeated below. The study was done on 1,259 college students, 825 of whom self-identified as having eaten breakfast before taking the exam. What can you say about the number of students who got D's and E's in each of the two groups?

the breakfast group have more D's and E's

Gastric freezing used to be used as a treatment for stomach ulcers. Physicians justified the use of this treatment based on interviews with patients, pre and post treatment that revealed an improvement, on average, in patient discomfort. The problem with this experimental design was that

the design did not allow any placebo comparisons

Confounding often defeats attempts to show that one variable causes changes in another variable. Confounding means that

the effects of two or more variables are mixed up, so we cannot say which is causing the response

which of the following statements is true?

the mean and standard deviation are sensitive outliers.

An experiment is done to compare two methods of instruction, Method A and Method B. At the end of the experiment a statistician reports a p-value of 0.001. This means:

the methods are probably different

which of the following statements do you think could possibly be true?

the number of students enrolled at Midville University decreased by 10.4% last year

Read the article by Dr. Justin Lehmiller, below. This difference in distance they refer to was said to be "statistically significant" in a follow up to this article. What does statistical significance mean in the context of the article? In the article "DOES OXYTOCIN HELP MEN STAY FAITHFUL TO THEIR WIVES?" (November 19th, 2012), by Dr. Justin J. Lehmiller, we read (paraphrased): In a new study published in The Journal of Neuroscience, 86 heterosexual men either received three puffs of a nasal spray containing oxytocin or a placebo solution. Approximately half of the men were currently involved in a monogamous romantic relationship and the other half were single. Forty-five minutes after receiving the spray, participants were asked to ... interact with an attractive female research assistant in person. As part of this interaction, subjects had to choose the ideal distance to stand from her. (Partnered) men who received the placebo maintained a distance of approximately 21-24 inches. Partnered guys (on the oxytocin treatment) stayed an average of 27 to 31 inches (68-79 cm) away. So oxytocin therefore prevents cheating, right? Not exactly. First, there was no actual measure of infidelity or even temptation to cheat. We're just assuming that how far they stood (is a proxy) for temptation. To demonstrate that oxytocin actually reduces cheating, we would need a long-term clinical trial in which guys in relationships are given oxytocin or a placebo and then we would see who reports cheating more over a specified period of time. Second, is keeping an extra 6 or 7 inches away from someone who is really hot actually going to ensure fidelity? It's not like the guys who got oxytocin ran away screaming—they just stood back an extra couple of inches.

the physical distance men stayed from the "attractive woman" was enough larger for the oxytocin men than for the placebo men that it was likely not due to chance

You ask a question to a random sample of 1000 adults in California (population 38.3 million people) and to a separate random sample of 1000 adults in Indiana (population 6.6 million people). You make separate 95% confidence statements about the percent of all adults in each state who agree. Your margin of error for Indiana is: (you may find the following generic confidence interval information useful)

the same as in California, because the two samples are the same size

How do you know that the subjects in the Brains and Beats study (BN 1.15) could not have been randomized to the treatments that were compared? This was one of the more widely-reported studies that supported music training as positively impacting general academic performance.

the treatments were at two separate schools and two separate points in time

Reporting the results of a medical experiment, researchers claim that the difference between two headache treatments is "statistically significant." What seems to be the alternative hypothesis here?

the two headache treatments do not preform equally well.

what is sampling variability?

the variability seen in statistics from sample to sample

In BN1.16 (or on the video version) on Comparison and Randomization we discussed an aids drug (Ribavirin) that the FDA ended up rejecting. What was wrong with the experimental design that the company used?

there was evidence that the sickest patients had been assigned to the placebo group

A researcher did experiments with six sets of animals with each set having five animals each. In a paper accepted into the Journal of Experimental Medicine the researcher reported the percentage of each set of five that had successful outcomes. Here are the numbers this guy reported: 53, 58, 63, 46, 48, and 57. What is wrong with these numbers?

they can't be results on sets of five animals unless they are multiples of 20 percent

what is "response substitution?"

this is the tendency for survey respondents to present their answers in a way that allows them to express their opinions about other issues that aren't topic of the survey

The well-respected journal Science, in an article on insects and plants, mentioned a California field that produced 750,000 melons per acre. How do you react to that? It may help you know that an acre is 43,560 square feet.

this is unreasonable, suggesting about 17 melon per square foot

Please read the following article from CBS News. The headline on this article refers to the "Majority of Americans." Assuming this means "ALL Americans" is the headline statistically defensible? Title: Poll: Majority of Americans Back Stricter Gun Laws Authors: Sarah Dutton, Jennifer De Pinto, Anthony Salvanto, Fred Backus and Leigh Ann Caldwell Source: CBS News January 17, 2013 As the president outlined sweeping new proposals aimed to reduce gun violence, a new CBS News/ New York Times poll found that Americans back the central components of the president's proposals, including background checks, a national gun sale database, limits on high capacity magazines and a ban on semi-automatic weapons. Asked if they generally back stricter gun laws, more than half of respondents—54%—support stricter gun laws ... That is a jump from April—before the Newtown and Aurora shootings—when only 39% backed stricter gun laws but about the same as ten years ago. ... This poll was conducted by telephone from January 11-15, 2013 among 1,110 adults nationwide. Phone numbers were dialed from samples of both standard land-line and cell phones. The error due to sampling for results based on the entire sample could be plus or minus three percentage points.

yes because 54% +/- 3% does not overlap 50%; so you are, in sense, 95% sure that p is bigger that .5 (50%)