Lecture 24-25: Cross-Sectional Studies Flashcards

1
Q

Give the definition of a cross-sectional study

A
  • Cross-Sectional studies are OBSERVATIONAL studies that examine relationships of health/disease to other variables of interest AT THE SAME TIME
    • a.k.a.; a PREVALENCE study
  • Entire population or a subset is selected for study
  • Called CROSS-SECTIONAL because information gathered represents what is occurring at a point in time or time-frame A-CROSS a large population. A “snap-shot” in time
  • Focuses SIMULTANEOUSLY on disease & population characteristics, including exposures, health status, health-care utilization, etc… (depending on study)
  • Seeks associations (NOT Causation)
  • Generates and tests hypotheses
  • By repetition in different time periods, can be used to measure change/trends (not in same patients)
  • Most Cross-Sectional studies are SURVEYS or DATABASESE capturing different aspects of US pop.
  • Data from different perspectives (e.g., inpatient vs. outpatient) or via different study/survey methodologies and information captured
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2
Q

Describe the two possible cross-sectional approaches

A
  1. Collect data on each member of the population
    - Pregnancy-Smoking data from KC Health Dept.
    - More frequently utilized in city/state-level evaluations, if data already tracked (ongoing collection)
    - Pregnancy-Smoking data from KC Health Dept.
    - More frequently utilized in city/state-level evaluations, if data already tracked (ongoing collection)
  2. Take a sample of the population & draw inferences to the remainder (generalizable)
    - More frequent approach (for U.S.-level data)
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3
Q

What is the most common sampling scheme?

A
  • Probability samples (most common)

- Every element in the population has a known (non-zero) probability of being included in sample

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4
Q

What are the 6? Examples of Probability Schemes?

A
  1. Simple
  2. Systematic
  3. Stratified Simple
  4. Stratified Disproportionate
  5. Multi-Stage
  6. Custer Multi-Stage
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5
Q

Describe Simple Random Sampling

A
  • Simple Random sampling
  • Assign random numbers, then take randomly selected numbers to get desired sample size, OR
  • Assign random numbers, then sequentially-list numbers and take desired sample size from top (or bottom) of listed numbers
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6
Q

Describe Systematic Random Sampling

A

Assign random numbers, then randomly sort these random numbers, then select highest (or lowest) number, then SYSTEMATICALLY , then by a pre-determined sampling-interval take every Nth numbers to get desired sample size

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7
Q

Describe Stratified Simple Random Sampling

A

STRATIFY Sampling Frame by desired characteristic (e.g., Gender), then use SIMPLE Random sampling to select desired sample size

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8
Q

Describe stratified disproportionate random sampling

A
  • Disproportionately utilizes STRATIFIED SIMPLE random sampling when baseline population is not at the desired proportional percentages to the referent population
  • Stratified sample ‘weighted’ to return sample population back to baseline population
  • Useful for ‘Over-Sampling’
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9
Q

Describe Multi-Stage Random Sampling

A
  • Uses SIMPLE Random sampling at MULTIPLE-STAGES towards patient selection
  • Counties (Primary Sampling Unit; PSU)
  • City Blocks/Zip Codes (Secondary Sampling Unit; SSU)
  • Clinic/Hospital/Household
  • Individual/Individual Chart
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10
Q

Describe custer multi-stage random sampling

A
  • Same as Multi-Stage Random sampling but ALL ‘elements’ clustered together (at any stage) or selected for inclusion
  • ALL Clinics in a zip code
  • ALL Households in a community
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11
Q

Describe Non-Probability Sampling Schemes

A
  • ‘Quasi-Systematic’ or ‘Convenience’ samples (not really, Completely Random or fully Probabilistic)
  • Decide on what fraction of population is to be sampled and how they will be sampled
  • Example: All persons whose last name begins with “M-Z”
  • Example: All members of a professional business association
  • Example: All persons attending clinic every M/W/F for 6 months
  • Example: All persons referred by selected-peers
  • Concern: There is some known or unknown order to the sample generated by selected scheme which may introduce bias (SELECTION BIAS)
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12
Q

Describe Two Common Broad Approaches to Collection of Study Data/Information

A
  1. Questionnaires/Surveys
    - Either directly from patients/caregivers or their medical records
  2. Physical assessments (which might involve laboratory, clinical, or psychological tests)
    - Great for assessing health/disease in similar population as time changes
    - NOT likely to be the same individuals year-to-year
    - Many U.S. Cross-Sectional studies are survey-based products of National Center for Health Statistics (NCHS), division of the Centers for Disease Control & Prevention (CDC)
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13
Q

What are advantages of cross-sectional studies

A
  • Quicker & easier for the RESEARCHER when using data already collected (compared to original data collection)
  • Data already collected & deidentified (Exempt IRB approval)
  • Less expensive for RESEARCHER than any form of prospective study
  • Can be analyzed like a Case-Control or Cohort study (group allocation)
  • Useful for estimating PREVALENCE rates
  • Useful for answering research questions about a myriad of elements
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14
Q

What are disadvantages of cross-sectional studies?

A
  • Prevalent cases may represent survivors
  • Difficult to study diseases of low frequency
  • Unable to generate Incidence rates
  • Problems in determining temporal relationship of presumed cause & effect
  • Due to the fact that exposure & disease histories are taken at the same time
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15
Q

What are Some Examples of Cross-Sectional Surveys from the NCHS? (National Center for Health Statistics)

** Kind of a big one

A
  • National Health and Nutrition Examination Survey (NHANES)
  • National Health Interview Survey (NHIS)
  • National Ambulatory Medical Care Survey (NAMCS)
  • National Hospital Care Survey (NHCS)
  • Behavioral Risk Factor Surveillance System (BRFSS)
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16
Q

Describe the NHANES

A
  • Assesses the health & nutritional status of adults & children
  • Combines interviews & physical examinations oInterviews include demographic, socioeconomic, dietary, & health-related questions
  • Examination component consists of medical, dental, physiological measurements & laboratory tests
  • Survey sample is selected to represent the US population of all ages
  • Oversamples persons
  • 60 years old, Blacks/African Americans & Hispanics
17
Q

Describe the NHIS

A
  • Principal source of information on HEALTH OF THE CIVILIAN, NON-INSTITUTIONALIZED POPULATION
  • Survey sample is selected to represent the US population of all ages
  • Has central role in other surveys such as the National Survey of Family Growth (NSFG) & the NAMCS/NHCS
  • Data are collected through a personal household interview (Broad range of health topics)
  • Consists of a set of core questions that remain largely unchanged & a set of supplements used to respond to public health data needs as they arise
18
Q

Describe the NAMCS

A
  • A national survey designed to meet the need for objective, reliable information about the provision and use of AMBULATORY MEDICAL CARE SERVICES in the United States
  • Based on a sample of visits to non-federal, office-based physicians primarily engaged in direct patient care
19
Q

Describe the NHCS

A
  • A combined national survey designed to describe national patters of healthcare delivery in NON-FEDERAL HOSPITAL-BASED SETTINGS, including:
  • Discharges from inpatient departments and institutions, & visits to emergency departments, outpatient departments and ambulatory surgery centers
  • Integrates 3 previous cross-sectional surveys:
  • National Hospital Discharge Survey (NHDS)
  • National Hospital Ambulatory Medical Care Survey (NHAMCS)
  • Drug-Abuse Warning Network (DAWN)
20
Q

Describe the BRFSS

A
  • A state-based system of telephone health surveys that collects information on health risk BEHAVIOURS, preventive health PRACTICES, and health care ACCESS primarily related to chronic disease and injury
  • Monthly data collection in all 50 states, DC, Puerto Rico, US Virgin Islands, & Guam
  • > 506,000 adults (>18 years old) are interviewed by telephone (2014) … Largest landline telephone health survey in the world
  • Youth BRFSS conducted by questionnaire in schools