Week 1 - Risk & Screening

Question 1

What is the aim of Epidemiology?

Answer 1

Basics:

• Study of Diseases

Components:

1. Understand - diseaes/health in population/community
2. Describe - health status/trends
3. Explain - etiology/causes/transmission
4. Predict - treatments/interventions
5. Control - prolong health/prevent/eradicate
6. Develop - policy/protocol/procedures

Question 2

What is a Count or Frequency?

Answer 2

• a number, a numerator, cases

Question 3

What is the difference between Ratio, Proportion, and Rate?

Answer 3

Ratio

• a value obtained by dividing one number by another
  
  • Can have more than two terms, and denominator not necessarily refer to the whole.

Proportion

• a type of ratio (numerator part of denominator)
• Two variables or factors, one has a constant or consistent relationship with the other.
  
  • Direct, Inverse, Logarithmic, etc.
  • Denominator refers to ‘of total or ‘of the whole’

Rate

• a type of ratio
• has a numerator and denominator
• 3 key elements:
  
  • Frequency
  • Population
  • Time

Question 4

Population at Risk

Answer 4

• not every person ‘at risk’ of particular condition
  
  • Occupational injury, environmental illness
    
    • exposure dependent
  • Prostate cancer, uterine cancer
    
    • gender dependent
  • Tonsillitis, appendicitis
    
    • sx dependent
• Careful: denominator = Incidence Rates
  
  • often just the average populations are used

Question 5

Incidence vs. Prevalence

Answer 5

Incidence

• # of NEW cases
  • how many marbles you just tossed in

Prevalence

• # of TOTAL cases
  • how many marbles total in the bowl

Question 6

How are Crude Rates calculated?

Answer 6

Basics:

• Frequency (# of cases) divided by Population

Example:

• death rate = 35.6 per 1,000 persons (Community A)
• death rate = 28.9 per 1,000 persons (Community B)

Age-Adjusted Rates:

• theoretical (artificial, synthetic, smoothed) denominator
• ‘level the playing field’
• compare ‘apples to apples’

Question 7

What is Screening?

Answer 7

Basics:

• Presumptive identification of previously unrecognized condition

How this occurs:

• Conducted via procedures, exams, tests
  
  • Preliminary in design
  • Confirmation of diagnosis required
• additional tests, exams, evaluations

Note:

• “Don’t go looking if you don’t know what to do when you find it”

Question 8

When is Screening Useful?

Answer 8

1. Simple
   
   • test is easy to administer & learn
2. Rapid
   
   • procedure itself, results = available (immediate = ideal)
3. Inexpensive
   
   • lower cost = more likely program to be beneficial
4. Safe
   
   • primum non nocere (first, do no harm)
5. Acceptable
   
   • to the target group
     
     • ex: testicular cancer (palpation) was not effective but mammography (imaging) is effective

Question 9

What are the 3 items to consider to deem Screening Appropriate?

Answer 9

1. Social
   
   • important condition (community & individual)
   • diagnostic, interventions, treatments available
   • cost/benefit ration
   • public acceptance
2. Scientific
   
   • natural disease history
   • case definition
   • treatment policies, protocols
   • effectiveness or efficacy of prevention/treatment
   • high prevalence rate
3. Ethical
   
   • suitable, effective, impact, appropriate

Question 10

How are Reliability and Precision related?

Answer 10

Basics:

• ability to give consistent results on repeated usages
  
  • irrelevant if result correct, incorrect, positive, negative

Dependent upon:

• variability of condition
• variability of measurement tool/method

Question 11

Sources of Unreliability and Invalidity

Answer 11

1. Measurement bias
   
   • constant errors due to measurement device or method
     
     • objective: scale/blood pressure cuff
     • subjective: clinical fxn, pysch status
2. Halo/Horns Effect
   
   • directional patterns in evaluations or questionnaires
     
     • all aspects seen in positive or negative light
3. Social desirability
   
   • questionnaires, open-ended, self-assessments
     
     • answers reflect “ought to be” or what “would lik”

Question 12

What are the 4 Measures of Validity?

Answer 12

1. Sensitivity
   
   • correctly identify as diseased those actually with disease
   • denominator = condition present
2. Specificity
   
   • correctly identify as non-diseased those actually without the disease
   • denominator = condition absent
3. Predictive Value (+)
   
   • proportion true + of those screening as +
   • denominator = test positive
     
     • Probability that pos test result = a true pos
4. Predictive Value (-)
   
   • proportion true - of those screening as –
   • denominator = test negative
     
     • Probability that neg test result = a true neg