This exercise is based on summary statistics rather than raw data. This informat

Question

This exercise is based on summary statistics rather than raw data. This information is typically all that is presented in published reports. You can perform inference procedures by hand from the summaries. Use the conservative Option 2 (degrees of freedom the smaller of

n1 1 and n2 1)

for two-sample t confidence intervals and P-values. You must trust that the authors understood the conditions for inference and verified that they apply. This isn't always true.

Healthy men aged 21 to 35 were randomly assigned to one of two groups: half received 0.82 grams of alcohol per kilogram of body weight; half received a placebo. Participants were then given 30 minutes to read up to 34 pages of Tolstoy's War and Peace (beginning at chapter 1, with each page containing approximately 22 lines of text). Every two to four minutes participants were prompted to indicate whether they were "zoning out." The proportion of times participants indicated they were zoning out was recorded for each subject. The table below summarizes data on the proportion of episodes of zoning out. (The study report gave the standard error of the mean

s/

,

abbreviated as SEM, rather than the standard deviation s.)

(a) What are the two sample standard deviations? (Enter your answers to two decimal places.)

(b) What degrees of freedom does the conservative Option 2 use for two-sample t procedures for these samples?
df =  

(c) Using Option 2, give a 90% confidence interval for the mean difference (Alcohol Placebo) between the two groups. (Round your answers to two decimal places.)

Explanation / Answer

Part-a

SE=s/sqrt(n)

So,, s=SE*sqrt(n)

Hence, s1=0.05*sqrt(25)=0.25 and s2=0.03*sqrt(25)=0.15

Part-b

Df=min(n1-1,n2-1)=min(25-1,25-1)=24

Part-c

For 90% CI, critical t=1.711

90% CI= (0.29-0.10)±1.711*sqrt(0.052+0.032)

=(0.0902          0.2898)

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.