Hss4303b – intro to epidemiologyApril 1, 2010 – a hodgepodge of stuff

Last time…

• Type I error– Incorrectly rejecting the null

• Type II error– Incorrectly failing to reject the null

Last time

• Alpha relates to Type I error– Typically set at 0.05

• Beta relates to Type II error– Typically set at 0.20

Power = 1- beta

Last time

• For 1-group study, and with alpha=0.05 and beta=0.20

N = 8 sigma2 / delta2 (approximately)

Last time

• For 2-group study, and with alpha=0.05 and beta=0.20

N per group = 16 sigma2 / delta2

(approximately)

Last time

• What is delta?– The smallest difference worth detecting

Example

• A cohort of 25 people is given an IQ test and scores an average of 138. After one year of intensive education, a similar IQ test is re-applied. The literature suggests that the standard deviation of the change in IQ should be 5. What is the smallest change in IQ that the cohort will be able to detect?

Delta = square root [8variance/N] = square root [8x25/25] = 2.8

Posters

Your posters

• New document uploaded to website• Poster is a visually presented research paper, but isn’t

just a paper pasted onto a wall• Half of the 25 marks I will assess before the poster day• The other half will be awarded by judges on the day• I need to receive via email the text of your posters (just

the text!) by midnight Thursday April 8th

– Send to hss4303@gmail.com– Failure to send on time will be penalized 2.5 of the total 25

marks for each 24 hour period it is late

From association to causation

• Approaches to etiology• Types of etiological associations• Types of causal relationships• Evidence of causal relationship• Examples of causal relationship– Peptic ulcers and gastric cancers– Alcohol use and abuse– Estrogen use and Alzheimer’s disease

Approaches to etiology

• In-vitro studies– Cell culture or organ cultures

• In-vivo studies– Animal studies• Acute exposures• Chronic exposures

– Human studies• Unplanned experiments• Natural experiments

Etiological studies

• Approaches to studying disease etiology– Animal studies– In-vitro studies– Population studies• Observation studies

– Chernobyl disaster– Bhopal tragedy– Hiroshima and Nagasaki study

Association studies

• Examination of association– If there is association; nature of this association

Observed association between exposure and disease

Anatomy of etiological studies

A frequent sequence of studies in human populations.

Ecologic studies

Correlation between dietary fat intake and breast cancer by country

Ecologic studies

• ____________ studies– Show plausibility of relationship– Does not establish causality– Does not take into account variability of exposure

among individuals– Ecologic fallacy• Ascribing to members of a group, characteristics that

they in fact do not possess individually

Causal relationship

• Types of causal relationships– Direct

• A factor directly causes a disease

– Indirect• A factor causes a disease through intermediate factor or factors

Different possibilities of causal relationship

• Necessary and sufficient• Necessary but not sufficient• Sufficient but not necessary• Neither sufficient nor necessary

Host

MediumAgent

Possibilities in causal relationship

1. Necessary and sufficient• A one to one relationship of exposure to disease, rarely if ever occurs

• Infection with corona virus H5N1 and development of SARS

Types of causal relationships: I. A factor is___________________________.

Possibilities in causal relationship

2. Necessary but not sufficient• One or more factors are essential and necessary, but not, in itself, sufficient to cause the disease• An initiator and promoter are both necessary to cause cancer but each on its own do not cause

cancer

Types of causal relationships: II. Each factor is ________________________.

Possibilities in causal relationship

3. Sufficient but not necessary• One or more factors (by themselves) can cause the disease• Radioactivity exposure or benzene exposure can each produce leukemia without

the presence of the other

Types of causal relationships: III. __________________________________.

Possibilities in causal relationship

4. Neither sufficient nor necessary• A complex interaction between factors, so no essential or required factors can be

identified• Hormonal changes, xenobiotics, chronic inflammation, dietary factors and age

are intricately involved in the development of prostate cancer

Types of causal relationships: IV. __________________________________________.

CSEB

• We welcome student members• The latest newsletter is now on the class

website– Features articles by your TA and one of your

classmates

Epidemiology around the world

http://www.youtube.com/watch?v=AW-ZHpFrLZQ

CAREC

WHO Epidemiology

• http://www.who.int/topics/epidemiology/en/

• Fact sheets• Global health atlas• Weekly epidemiology report• etc

Weekly Epidemiology Record

• http://www.who.int/wer/en/• “The Weekly Epidemiological Record (WER)

serves as an essential instrument for the rapid and accurate dissemination of epidemiological information on cases and outbreaks of diseases under the International Health Regulations and on other communicable diseases of public health importance, including emerging or re-emerging infections. “

The CDC

• Lots of fun tidbits on their website:– www.cdc.gov

CDC Tracking network:– http://www.youtube.com/watch?v=J42CLZH1NlE

CDC outbreak response– http://www.cdc.gov/CDCTV/RespondOutbreaks/

index.html

Epi Info

• Free epidemiology software created by the CDC

• http://www.cdc.gov/epiinfo/

Erin’s Hours

• No more formal tutorials except for two exam review sessions:– April 22– April 26 (afternoon)