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1

Which of the following is an advantage of a retrospective case-control study?

1.There is little or no bias in the recall of exposures

2.Multiple disease outcomes following a selected exposure can be studied

3.Ideal to investigate rare diseases in a relatively short period of time

4.It is the study design of choice to investigate risk factors of a common disease

1.Ideal to investigate rare diseases in a relatively short period of time

2

•Why use Study Designs?

  -   To investigate the association between exposure   and   disease with efficient use of resources

  -    To collect information in an organized, systematic   and meaningful way

•Why use Study Designs?

  -   To investigate the association between exposure   and   disease with efficient use of resources

  -    To collect information in an organized, systematic   and meaningful way

3



Study Design 1. Prospective Cohort studies
 

•Observational studies

___ ___ temporality between exposure and disease

•Aim: Compare disease rates for two or more ___



Study Design 1. Prospective Cohort studies
 

•Observational studies

•Can establish temporality between exposure and disease

•Aim: Compare disease rates for two or more cohorts

4

Prospective Cohort studies
Strengths & Limitations

•Strengths

  - Temporality__ ___ established

  - Investigator determines the ___ (exposure and outcome have already occurred)

  - Multiple ___ can be studied

•Limitations

  - ____

  - Loss to __ ___with long periods of time


-Difficult sample selection

   -Changes overtime for both exposure and outcomes

•Strengths

  - Temporality can be established

  - Investigator determines the cost (exposure and outcome have already occurred)

  - Multiple outcomes can be studied

•Limitations

  - Expensive

  - Loss to follow-up with long periods of time


-Difficult sample selection

   -Changes overtime for both exposure and outcomes

5

Study Design 2:

Retrospective Case-Control Studies

•Examines multiple____ in relation to a disease

•Subjects are defined as ___ and ___•

•Exposure ___ are compared

•Retrospective study; challenging control ___

__ ___ way to examine __ disease (when compared to cohort studies)

•Sometimes challenging for subjects to ___  past exposures and error in answering questionnaires can be a serious limitation in this study design

•Examines multiple exposures in relation to a disease

•Subjects are defined as cases and controls

•Exposure histories are compared

•Retrospective study; challenging control selection

•Cost-effective way to examine rare disease (when compared to cohort studies)

•Sometimes challenging for subjects to recall past exposures and error in answering questionnaires can be a serious limitation in this study design

6

Study design: Cross-sectional studies'

•An “observational” design that surveys___ and ___  status at a s____e point in time  (a cross-section of the population)

Cross section al studies are some of the __studies completed because of ___ and__ __

•An “observational” design that surveys exposures and disease status at a single point in time  (a cross-section of the population)

Cross section al studies are some of the first studies completed because of  ease and low cost

7

Cross-sectional Studies

•Often used to study conditions that are relatively ___t with ___ duration of expression (+____, ___ conditions)

•It measures ___, not ___ of disease

•Example: community survey

 

Cross-sectional studies involve ___ prevalence, not incidence.  For very____t diseases they are of  limited utility

Know prevalence vs incidence for exam!

•Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression

Cross-sectional Studies

•Often used to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions)

•It measures prevalence, not incidence of disease

•Example: community surveys

 

Cross-sectional studies involve point prevalence, not incidence.  For very infrequent diseases they are of  limited utility

Know prevalence vs incidence for exam!

•Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression

8

Cross-sectional studies - Disadvantages

___ observational design  

•It measures prevalence, not incidence of disease

•Prevalent cases are ___

•The temporal sequence of exposure and effect may be ___ or___ to determine

•Usually don’t kno___ n disease occurred

–

–

•Weakest observational design 

                       

•It measures prevalence, not incidence of disease

•Prevalent cases are survivors

•The temporal sequence of exposure and effect may be difficult or impossible to determine

•Usually don’t know when disease occurred

–

–

9

Data source

•SEER – ___ ____ ___ ____

•Coordinated system of____ registries

-Patient demographics

-Tumor site

-Specific cancer markers

-Cancer stage at diagnosis

-First course of treatment

-Survival

•SEER – Surveillance, End and Epidemiological results

•Coordinated system of cancer registries

-Patient demographics

-Tumor site

-Specific cancer markers

-Cancer stage at diagnosis

-First course of treatment

-Survival

10

SEER – Surveillance End and Epidemiology Results

•Covers ___% of the US population

•Funded b___ __ __ and __ __ __

•Covers 28% of the US population

•Funded by National Cancer Institute and CDC

11

Causation- What is a Cause? 

•Causality is the relationship between an event (the cause) and a second event (the effect), where the second event is a consequence of the first.
en.wikipedia.org/wiki/Cause

•KJ Rothman: An event, condition, or characteristic without which the disease would not have occurred.

•Causality is the relationship between an event (the cause) and a second event (the effect), where the second event is a consequence of the first.
en.wikipedia.org/wiki/Cause

•KJ Rothman: An event, condition, or characteristic without which the disease would not have occurred.

12

Bradford Hill’s criteria 
 

1. T___ * – exposure has preceded the disease in time;

2. C ____* – reported from different investigations;

3. S____h* – the stronger the association the less likely it is due to a biasing factor;

4. B___ ____nt – follows a currently accepted pathobiologic process

5. S___ – one effect? Many effects?

6. P___ - with existing knowledge

7. C___ * – compatible existing theory and knowledge

8. E__ __ –  condition can be altered

9. A___– consider the effect of similar factors

1. Temporality * – exposure has preceded the disease in time;

2. Consistency * – reported from different investigations;

3. Strength* – the stronger the association the less likely it is due to a biasing factor;

4. Biologic gradient – follows a currently accepted pathobiologic process

5. Specificity – one effect? Many effects?

6. Plausibility- with existing knowledge

7. Coherence * – compatible existing theory and knowledge

8. Experimental Evidence –  condition can be altered

9. Analogy – consider the effect of similar factors

13

•“Cause” is different from association of exposure to health outcomes

•“Correlation does not imply causation”

•“Cause” is different from association of exposure to health outcomes

•“Correlation does not imply causation”

14