Some of your questions/thoughts Why are we more afraid of some things than others? Who is responsible for making sure that numbers and statistics are reported.

Some of your questions/thoughts

Why are we more afraid of some things than others?

Who is responsible for making sure that numbers and statistics are reported accurately?

Why are Americans so prone to quoting statistics? Does it really make a difference in our behavior?

How does the epidemiological definition of risk interact with other definitions of risk we have encountered?

How do we determine which sources are credible and which are not so credible?

How do we make sense of health statistics?

Overview of Today 1) Go back to exercise from last week and correct mistakes

2) Story about how this course came together

3) Context

4) Medical Data Interpretation Test

Prompt for Journal Entry 2 ***Be sure to have an engaging title Prompt: Talk with a roommate/friend who is not in the class for about 15-20 minutes. Try to explain the differences between the study designs to your colleague. Try to use examples beyond what we discussed in class. How did you use the class readings/texts to help with your discussion? In your post, describe how the interaction went—what types of examples did you use? What questions did the friend ask? What questions came to your mind as you tried to explain the concepts?

In the tag, include the entry Journal entry #2

Comment on 1-2 of your peers articles

(Follow word count and Honor Code guidelines as described for Journal Entry 1)

Activity: How do we relate two quantities?

Some facts:

1) In the year 2000, there were 275,306,000 people in America

2) 151,268 DIED of external (non-disease) related activities

3) The life expectancy of an individual is 76.9 years

occurringnot event ofy Probabilit

occurringevent ofy ProbabilitOdds

Depends on a definition of the eventFor example, in sports betting…

winningofy Probabilit

winningNOT ofy ProbabilitOdds

Case control study

ODDS in our example!!! One year Odds:

◦ Numerator= # of people in America who were alive

◦ Denominator= # people who died from that disease

Ex. Drowning : 275306000 people alive /3248 died of drowning

79,065 people alive/1 died of drowning

Odds of death by drowning is 1 in 79,065

Lifetime odds: One year odds DIVIDED by the life expectancy i.e. 79065/76.9= 1028

Note: this is not the same as the proportion of deaths.

Proportion of deaths= Death from drowning/Death from all other causes;

3248 people died from drowning/ 151,268 DIED in America of external causes= 0.021*100%= 2.1%

2.1% of people who died of EXTERNAL causes died from accidental drowning and submersion

Another example

Proportions involve comparing parts to a whole and can only be between 0 to 1. ◦ Proportion: Orange squares/all squares= 3/5=0.6

Odds can range from positive infinity to negative infinity. Odds: orange squares/brown squares= 3/2 or 1.5/1 ; The odds of picking an orange square is 1.5 times the odds of picking a brown square

Point: It’s tricky to know whether we are talking about odds or proportions

ASK QUESTIONS!!! Know what goes in the numerator and denominator of any fraction!!

This is why numeracy is important!

We will practice with this concept

How do we calculate these risks? STUDY DESIGN

Components of an epidemiological study

Population---need to define your population in terms of age, race, SES, etc. ; How many people will you try to recruit?

Disease—need a case definition

Time frame-How long will you follow people?

Study design- How will you collect information? How will you verify information? What resources do you have?

We will focus on observational study designs: cohort, case-control, cross-sectional

Take EPID 600 if you are interested in this stuff!

Ways to gather information1. Case study

2. Surveillance—Vital Statistics (Looking at death statistics)

3. Experimental studies (drug testing, randomized control trials, experiments)

4. Observational studies (cohort, case-control and cross-sectional)

Cohort Study

Cohort Study

Directionality: Always forwardData collection: Prospective or Retrospective

Cohort study

Yes (E+) No (E-)

Yes (D+) a b m1

No (D-) c d m0

n1 n0 N

Disease

Exposure

20

A cohort study: heart attack survivors after 5 years of follow up

Smoke Quit

Dead 27 14 41

Alive 48 67 115

Total 75 81 156

21

What is the 5-year risk of dying among the exposed? 0.36

What is the 5-year risk of dying among the non-exposed? 0.17

What is the ratio of the two risks? 2.1

What is the difference between two risks? 0.19

The ratio of two risksRisk Ratio (RR) a.k.a. Relative Risk

22

??smokingquit who thoseamongRisk

smokers continous amongRisk RR

Interpretation? Risk of disease in Exposed is 2.1 times the risk of disease in non-exposed, over 5 years.

exposednot amongRisk

exposed amongRisk

CI

CI

0

1 RR

P

POdds

1ocurringnot event ofy Probabilit

ocurringevent ofy Probabilit

Depends on a definition of the eventFor example, in sports betting…

winningofy Probabilit

winningNOT ofy ProbabilitOdds

Case control study

An easy way to calculate OR

Yes (E+) No (E-)

Yes (D+) a b m1

No (D-) c d m0

n1 n0 N

Disease

Exposure

24

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