Lecture Notes: Disease Frequency

Overview

• Previous Topic: Accuracy of screening and diagnosis methods
  • Key measurements: Reliability and Validity
  • Importance: All good studies should report reliability and validity

Study Methods for Disease Frequency

1. Cross-Sectional Surveys

   • Focus: Prevalence of disease in the population
   • Method: Random sample from a sampling frame
     • Sampling frame: Source of demographic or population information
     • Provides a snapshot of how much of a population has disease
   • Data Collection: Questionnaires or interviews
   • Target Population: Entire population of interest
   • Sample Population: A representative sample
   • Prevalence Calculation:
     • Formula: Diseased individuals/Total population
     • Reported as a percentage or decimal
   • Case Definition: Categorization of disease presence or absence
   • Severity: Improved measurement over binary presence/absence
     • Uses disease indices like DMFT (Decayed Missing Filled Teeth Index)

2. Prospective Cohort Studies

   • Focus: Incidence of disease in a population
   • Method: Random sample from a healthy at-risk population
     • Baseline and follow-up assessments to track new disease development
   • Incidence Calculation:
     • Formula: New cases/Population at risk
     • Expresses the probability of developing disease

3. Case Studies

   • Focus: Rare conditions in individuals
   • Method: Report interesting or unknown cases

Important Concepts

• Sampling Variability/Error:

  • 95% Confidence Interval: Likely range of population estimate
  • P-Value: Type 1 error probability; lower values indicate meaningful results
  • Increasing sample size reduces sampling variability

• Convenience Sampling:

  • Non-random sampling leading to potential bias
  • Issues: Incomplete data due to non-response, differing response rates

Statistical Considerations

• Importance of equal group sizes for valid comparisons
• Non-overlapping confidence intervals indicate statistically significant differences

Next Topic: Etiology

• Discussion on the third major aspect of disease studies

• Note: Etiology will be covered in the next video.