New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here

Intrmd Biostatistics

by: Agustin Bechtelar

Intrmd Biostatistics PUBHLTH 640

Agustin Bechtelar
GPA 3.88


Almost Ready


These notes were just uploaded, and will be ready to view shortly.

Purchase these notes here, or revisit this page.

Either way, we'll remind you when they're ready :)

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

Class Notes
25 ?




Popular in Course

Popular in Public Health

This 6 page Class Notes was uploaded by Agustin Bechtelar on Friday October 30, 2015. The Class Notes belongs to PUBHLTH 640 at University of Massachusetts taught by Staff in Fall. Since its upload, it has received 13 views. For similar materials see /class/232294/pubhlth-640-university-of-massachusetts in Public Health at University of Massachusetts.


Reviews for Intrmd Biostatistics


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 10/30/15
Puleth 640 Unit 1 Review of Puleth 540 Introductory Biostatistics Intermediate Biostatistics Practice Problems Week 1 SOLUTIONS 1 Recall that variables can be of different types We learned in introductory biostatistics that appropriate methods of summarization depend on the variable type And we noticed that sometimes a method of summarization is not appropriate For example it is not appropriate to construct a cumulative frequency graph summary of nominal data Using whatever sources you have for introductory biostatistics complete the following table Random Variable Discrete Continuous Nominal O inal Interval Ratio Descriptive Methods Bar chart Bar chart Ple Chart Ple Chart Dot diagram Dot diagram Scatter plot 2 variables Scatter plot 2 variables Stem Leaf Stem Leaf Histogram Histogram Box Plot Box Plot Quantile Quantile Plot Quantile Quantile Plot Numerical Summaries Freq Table Freq Table Rel Freq Table Rel Freq Table Cum Freq Table Cum Rel Freq Table means variances percentiles means variances percentiles Wklisolutionsdoc Intermediate Biostatistics Try your hand at the following probability exercises a Divide a line segment into three parts such that one portion is half the length of original line and the other two portions are each one quarter then length of the original line Choose a point at random What is the probability that this point is in the 12 length portion Answer 5 Solution As all points along the line segment are equally likely length is pr0p01ti0nal t0 probability Thus 12 length corresponds to 12 0f the total probability b If there is a 14 chance that any person selected at random was born on a Monday what is the probability that of any seven people selected at random exactly one was born on a Monday Answer 40 Solution This is a binomial probability calculation X Realized count of number of Monday birthdays in sample of 7 N trials 7 Event of interest is birthday on a Monday TE Probabilityevent l4 Calculate Pr X 1 3965 1 11 1 nhm c What are the odds of getting exactly one pair in ve card stud poker using a 52 card deck Answer Odds are 42 to 58 Solution This is a combinatorial calculation that assumes all ve card hands are equally likely probabilit exac y one pair hands that are exactlyone pa1r Total hands poss1ble total hands possible 52 W 2 598 960 5 5 47 5432l To solve for the hands that are exacth one pair the idea is to think in steps 1 choices ofa rank ace 0r 2 0r 3 0r 0r queen 0r king 13 Wklisolutionsdoc Puleth 640 Intermediate Biostatistics 2 For selected rank choices of suits to be in the pair 4 i m 2 22 20 3 Now think about the remaining 3 cards They have to be of distinct ranks else hand will no longer be exactly one pair choices of distinct ranks for 12 12 121110 the other 3 cards from the leftover 12 ranks 220 3 3l9 321 4 Finally recognize that for each rank you also get to choose its suit choices for suit of 1st of remaining 3 cards 4 5 Similarly choices for suit of 2nd of remaining 3 cards 4 6 Last but not least choices for suit of 3rd of remaining 3 cards 4 Putting these all together gives us the count of the hands that are exactly one pair Count 136220444 1098240 So now we can solve hands that are exactly one pair 7 l 098 240 7 042257 Total hands p0551ble 2 598 960 probabilityexactly one pair 042257 7042257 1042257 057743 Thus odds exactly one pair d Suppose a quiz contains 20 truefalse questions You know the correct answer to the rst 10 questions You have no idea of the correct answer to questions 11 through 20 and decide to answer each using the coin toss method Calculate the probability of obtaining atotal quiz score of at least 85 Answer 18 Solution This is also a binomial probability calculation X Count of correct answers among questions 11 20 N trials 10 A grade of 85 or better corresponds to 8520 17 correct or more Thus among questions 11 20 you must be correct 7 or more times TE Probabilitycorrect answer 50 Calculate Pr X 3 7 171875 1 1 1171 39 39quotlnml Wklisolutionsdoc Puleth 640 Intermediate Biostatistics 3 Refresh your memory of the elements of a con dence interval There are three 1 point estimate 2 standard error of the point estimate and 3 con dence coef cient Complete the following summary table Normal Distribution Confidence Interval for ul u Two Independent Groups CI point estimate i confcoeffSEpoint estimate 039 and 039 are both 039 and 039 are both NOT 039 and 039 are both known known but are assumed NOT known and NOT EQUAL Equal EStmate XGroup l XGroup 2 XGroup l XGroup 2 XGroup l XGroup 2 SE to use swamp 59ml if 2 sEP iGml 72W s gt ltemupltW S 1S 2 n1 n2 n1 n2 n1 n2 where you already have obtained S2 7 n1ils12n2 TDS p001 7 n1 Tln2 71 Confidence Normal Student s t Student s t Coef cient Use Percentiles from 2 S2 S2 1 2 f 111 n 2 Degrees Not applicable n1 1 n2 1 2 2 2 2 freedom 8 1 i n n 1 2 n1 1 n2 1 Wklisolutionsdoc Puleth 640 Intermediate Biostatistics 4 See if you can recall some of the important concepts that are discussed in introductory biostatistics a What is a sampling distribution Answer A sampling distribution is a probability distribution for a random variable that is itself a statistic Thus sampling distributions refer to the probability distributions of such things as the sample mean the sample variance etc These probability distributions are the result of the idea of replicate sampling infmitely many times b What does the central limit theorem tell us Why is it so useful to us What is a zscore What is a tscore Answer The central limit theorem tells us that as the choice of sample size increases the sampling distribution of the average approaches normality This is very useful to us because it allows us even for moderate sample size to regard the average as a realization of a Normal distribution random variable Erandom variable zscore SErandom variable random variable Erandom variable t score Estimated SErandom variable c In a sentence or two explain the meaning of a 95 con dence interval for a population mean that has lower limit 356 and upper limit 528 Answer This interval allows the investigator to say that heshe is 95 con dent that the unknown true population mean is between 356 and 528 Of course the true mean is either in this interval or not we don t actually know Recall that it is NOT CORRECT to say that the probability is 95 that the population mean is between 356 and 528 Wklisolutionsdoc Puleth 640 Intermediate Biostatistics d De ne pvalue Interpret plt05 and plt01 Given identical study conditions which gives stronger evidence against the null hypothesis Answer A p value is a chance statement A p value is the probability that the test statistic of interest attains a value as extreme or more extreme relative to the null hypothesis under the null hypothesis probability model All other things being equal a p lt 01 gives stronger evidence against the null hypothesis e Suppose a two sided hypothesis test of treatment benefit in a randomized controlled trial of placebo versus active treatment yields a pvalue of 0045 What are the possible explanations for this result Answer There are several possible explanations and ultimately we do not know which one is the correct explanation Among them are The active treatment is truly different than the placebo The active treatment is equivalent to the placebo but an event of low probability has occurred The active treatment is equivalent to the placebo but one or more biases have biased the data in the direction of statistical signi cance albeit marginal Wklisolutionsdoc


Buy Material

Are you sure you want to buy this material for

25 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Bentley McCaw University of Florida

"I was shooting for a perfect 4.0 GPA this semester. Having StudySoup as a study aid was critical to helping me achieve my goal...and I nailed it!"

Kyle Maynard Purdue

"When you're taking detailed notes and trying to help everyone else out in the class, it really helps you learn and understand the I made $280 on my first study guide!"

Jim McGreen Ohio University

"Knowing I can count on the Elite Notetaker in my class allows me to focus on what the professor is saying instead of just scribbling notes the whole time and falling behind."

Parker Thompson 500 Startups

"It's a great way for students to improve their educational experience and it seemed like a product that everybody wants, so all the people participating are winning."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.