Epidemiological statistics II

1. Epidemiological statistics
Types of data used in epidemiological statistics
Sampling techniques in epidemiological studies
Dr. S. Parasuraman M.Pharm., Ph.D.,
Senior Lecturer, Faculty of Pharmacy,
AIMST University,
Bedong 08100, Malaysia.

2. Types of data used in epidemiological
statistics
• Demographic data
• Vital statistics data
• Surveillance data
• Health status and behavioral data
• Behavioral Risk Data
• Socioeconomic data
• Utilization data
• Dates of Events and Legislation Data
• Utilization data
• Health Economics Data
• Other Types of Data

3. Types of data used in epidemiological
statistics
• Demographic data:
– Used to determine the population-at-risk
– Primary source of demographic data is a census
• Vital statistics data
– Maintained by National Center for Health Statistics in the
Department of Health and Human Services through contracts of
agreement with states
– Collection of the data is the responsibility of the locality and the
state
– Birth data (natality)
– Death data (mortality)
– Marriage data
– Family history

4. Types of data used in epidemiological
statistics
• Surveillance data
– Race and Ethnicity in Public Health Surveillance
– Office of Management and Budget (OMB) category
• Health status and behavioral data
– National Health and Nutrition Surveys (NHANES I, NHANES II,
NHANES III, HHANES)
– Surveillance data (Morbidity and Mortality Weekly Report or
MMWR)
– National Health Interview Survey (NHIS)
– US Immunization Survey
– Registry Data (cancer, lead, birth defects)
– Individual or aggregate patient records

5. Types of data used in epidemiological
statistics
• Behavioral Risk Data
– Behavioral Risk Factor Survey (BRFS)
– Youth Risk Behavior Survey (YRBS)
– Patient interviews
– Alcohol, smoking, violence estimates
• Socioeconomic data
– Consumer Price Index
– GNP
– Employment rates
– Welfare status
– Inflation rates
– School attendance records
– Manufacturing and industrial data
• Utilization data

6. Types of data used in epidemiological
statistics
• Dates of Events and Legislation Data
– Voting records of legislators on health-related issues
– Dates of health fairs or publicity campaigns
• Utilization data
– National Hospital Discharge Survey
– National Nursing Home Survey
– National Ambulatory Medical Care Survey
– Surveys of Mental Health Facilities
– WIC
– Medicaid and Medicare records
– Third party payment records
– Hospital/clinic/office records
• Health Economics Data
– National Medical Care Expenditure Survey (NMCES)
– Medicaid and Medicare records
– Third party payment records

7. Types of data used in epidemiological
statistics
• Other Types of Data
• Clinical data
– Height
– Weight
– Blood pressure
– Presence of signs
and/or symptoms
– Autopsy findings
• Laboratory data
– WBC
– Hematocrit
– Cholesterol
– Lead levels
– pH levels
– bacteriology reports

8. Sampling techniques in epidemiological
studies
• Random sampling
• Multi-stage sampling
• Systematic sampling
• Purposive selection
• Convenience sample
• Stratification
• Paired sampling
• Sampling with and without replacement

9. Sampling techniques in epidemiological
studies
• Random sampling: A simple random sample (SRS) of
size n is produced by a scheme which ensures that
each subgroup of the population of size n has an
equal probability of being chosen as the sample.

10. Sampling techniques in epidemiological
studies
• Multi-stage sampling:
– Simple random sampling (SRS) is not possible with too
large population.
– Multi-stage sampling may
• Randomly select primary sampling units at the first
stage (specific communities, specific health facilities)
• Within the primary sampling units, randomly selected
the final sampling units at the second stage (drug use
encounters, patients, households)
• Sometimes in complex samples, additional stages are
needed that will be added further.

11. Sampling techniques in epidemiological
studies
• Multi-stage sampling:

12. Sampling techniques in epidemiological
studies
• Systematic sampling: Selection of elements form an ordered
sampling frame. The most common systemic sampling is an
equal-probability method using each element in the
population has a known and equal probability of selection.
• Systemic sampling is to be applied only if the given
population is logically homogeneous, because sampling units
are uniformly distributed over the population.

13. Sampling techniques in epidemiological
studies
• Stratification: Divide the population into "strata". There can
be any number of these. Then choose a simple random
sample from each stratum. Combine those into the overall
sample. That is a stratified random sample.
• Example: Church A has 600 women and 400 men as
members. One way to get a stratified random sample of size
30 is to take a SRS of 18 women from the 600 women and
another SRS of 12 men from the 400 men.

14. Sampling techniques in epidemiological
studies
• Purposive selection: A purposive sample, also commonly
called a judgmental sample, is one that is selected based
on the knowledge of a population and the purpose of the
study. A purposive sample is a non-representative subset
of some larger population, and is constructed to serve a
very specific need or purpose.
• Convenience sample: A convenience sample is a matter of
taking what you can get. It is an accidental sample.
Although selection may be unguided, it probably is not
random, using the correct definition of everyone in the
population having an equal chance of being selected.

15. Sampling techniques in epidemiological
studies
• Paired sampling: Also called as dependent samples. In
paired samples, each data point in one sample is matched
to a unique data point in the second sample.
• E.g.: Pre-/ post test study design; cross-over
pharmacokinetic study design of two different formulation
of same drug and bioequivalence studies.
Test the computer skills of
participants before and after
they complete a computer
training course.

16. Sampling techniques in epidemiological
studies
• Sampling with and without replacement :

17. Methods for obtaining data in
epidemiological studies
• Interviews and questionnaires
• Procedures involving measurements
• Errors due to observations and measurements

18. Measures for Statistical analysis of
epidemiological data
• The following measures should be for statically analysis of
epidemiological data
– Generalization of data must be ensured
– If data generated by other investigators, aware about significant omissions
or biases in the data (which may influence the analysis)
– Do not ignore the anomalies in data
– Avoid the temptation to use complicated statically techniques of the
quality of the data dose not warrant it
– Don’t afraid to record negative findings
– Limitations in the data should be clearly stated
– Ensure the data quality of data and study design
• Epidemiological statistics mainly focused on population parameter,
testing statistical hypotheses in large-size/ small size samples.

19. Thank you