Analysis of Medical Data Research Perspective

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Analysis of Medical DataResearch Perspective

• Nancy B. Clark. M.Ed.
• Director of Medical Informatics Education
• FSU College of Medicine
• Spring 2004

http//www.med.fsu.edu/informatics
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Objectives

• Review statistical concepts to be on Step 1.
• Determine what data exist relative to a clinical
  question or formal hypothesis
• use IT to locate existing data sources
• identify and locate existing data sets
• Within institution
• Outside institution
• Analyze, interpret and report findings
• Select and use appropriate computer software
  Excel, SPSS
• Use software to perform simple statistical
  analysis and portray results graphically
• Interpret reports

3
Prerequisite Skills (Step 1 USMLE)

• Fundamental concepts of measurement
• Scales of measurement
• Distribution, central tendency, variability,
  probability
• Disease prevalence and incidence
• Disease outcomes (eg, fatality rates)
• Associations (correlation or covariance)
• Health impact (eg, risk differences and ratios)
• Sensitivity, specificity, predictive values

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More Prerequisite Skills (Step 1 USMLE)

• Fundamental concepts of hypothesis testing and
  statistical inference
• Confidence intervals
• Statistical significance and type I error
• Statistical power and type II error  

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More Step 1 Topics

• Fundamental concepts of study design
• Types of experimental studies (eg, clinical
  trials, community intervention trials)
• Types of observational studies (eg, cohort,
  case-control, cross-sectional, case series,
  community surveys)
• Sampling and sample size
• Subject selection and exposure allocation (eg,
  randomization, stratification, self- -
  selection, systematic assignment)
• Outcome assessment
• Internal and external validity

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Scales of Measure

• Nominal qualitative classification of equal
  value gender, race, color, city
• Ordinal - qualitative classification which can
  be rank ordered socioeconomic status of
  families
• Interval - Numerical or quantitative data can
  be rank ordered and sizes compared temperature
  
• Ratio - interval data with absolute zero value
  time or space

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Distribution, Central Tendency
Mean
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Variability, Probability

• Mean
• Median
• Mode
• Standard deviation
• Statistical Significance p lt .01

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Confidence Interval
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Statistical SignificanceType I and Type II
errors
Null Hypothesis Ho
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Statistics Online Textbook

• The Statistics Homepage
• http//www.statsoftinc.com/textbook/stathome.html

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Disease Prevalence and Incidence

• Prevalence
• probability of disease in entire population at
  any point in time
• 2 of the population has diabetes
• Incidence
• probability that patient without disease develops
  disease during interval
• 0.2 or 2 per 1000 new cases per year

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Sensitivity, Specificity

• sensitivity a / (ac)
• specificity d / (bd)

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Predictive Value

• Positive predictive value a / ( ab)
• Negative predictive value d / (cd)
• Post-test probability of disease given positive
  test a / (ab)
• Post-test probability of disease given negative
  test c / (cd)

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Good Resource Sen, Spc, PV

• An Introduction to Information Mastery
• http//www.poems.msu.edu/InfoMastery/default.htm
• Diagnosis
• Sensitivity and specificity
• Predictive values
• Likelihood ratios
• InfoRetriever
• Calculators Epidemiology, Diagnostic test

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Fundamental Concepts of Study Design

• Good Resource
• Epidemiology for the Uninitiated
• BMJ
• Online Textbook
• http//bmj.com/collections/epidem/epid.shtml

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Finding Health Statistics
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Types of Health Statistics Questions

• Fact lookups
• Research
• Presentations
• Social and Policy indicators

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Strategies for Finding Health Stats

• Use Portal
• Start at Internet site
• Start with book or article

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Internet Portals of Health Stats

• Lists of links that provide starting points for
  browsing or searching
• Keyword search in portal vs Google
• General idea what you want
• The Related Health Services Research Web Sites
  http//www.nlm.nih.gov/nichsr/hsrsites.html
• The NCHS portal http//www.cdc.gov/nchs/

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Other Statistical Web Sites

• CDC Data and Statistics http//www.cdc.gov/scienti
  fic.htm
• FedStats Home Page http//www.fedstats.gov/
• Compare these two
• U Michigans Statistical Resources on the WEB
  HEALTH
• What type of stats

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Lexis-Nexis Statistical Universe

• Subscription resource
• Searches stat data
• Subject List
• Limit search
• Reports or tables
• http//web.lexis-nexis.com/statuniv?B1Connectto
  StatisticalUniverse

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MMWR

• Morbidity illness
• Mortality death
• http//www.cdc.gov/mmwr/
• Disease Trends
• Tables - searchable

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Health Care Data

• Healthcare Cost and Utilization Project
• HCUPnet
• Hospital discharges
• Ambulatory service
• Costs
• Amount of care
• By diagnosis and procedure
• Surveys of hosp, physicians, nursing homes

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Health Consequences

• Costs to society, individuals
• Cost from care
• Costs of illness
• Impact on infrastructure
• HCFAgtCMS Health Accounts
• http//www.cms.hhs.gov/statistics/nhe/default.asp

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State and International Data

• Floridahealthstat.com - Where Florida Health Data
  Resides
• DOH Epidemiology
• KFF State Health Facts Online
• United Nations Statistics Division
• World Health Organization Research Tools

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Individual Datasets

• EMR
• Billing
• CDCS
• Customized data collection tools

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Data Analysis
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Selecting the Appropriate Software

• Spreadsheet
• Numerical (interval or ratio) data
• Sums
• Averages
• Standard deviations
• Simple charts and graphs

• Statistical Software
• Nominal or Ordinal data
• Comparisons of two groups
• Frequency tables
• Complicated charts and graphs
• Normal curves
• Class intervals
• Statistical significance

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Spreadsheets

• Excel
• Pocket Excel

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Data Tables

• Field names at top
• Each row is a record (sample)
• Sorting whole table
• By one column
• By more than one column
• Sorting individual sections

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Descriptive Statistics

• Distribution
• frequency distribution
• Histogram
• Central tendency
• Mean
• Median
• mode

• Dispersion
• Range
• Standard deviation
• Variance
• N
• Not P (inferential stats)

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Central Tendency

• Mean
• AVERAGE(b2b1500)
• Median
• MEDIAN(A2A7)
• Mode
• MODE(A2A7)
• N
• COUNT(A2A1500)
• COUNTBLANK(A2B5)

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Dispersion

• Range
• MAX(A2A60)- MIN(A2A60)
• Standard deviation
• STDEV(A2A110)
• Variance
• VAR(A2A110)

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Distribution

• Frequency distribution
• Not easy use SPSS
• FREQUENCY(data_array,bins_array)
• Use help
• Histogram
• Bar chart of frequency table

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Hands on experience

• Analyze data in examples2.xls

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Statistical SoftwareIntro to SPSS
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Statistical Software

• SPSS
• Provided by request/justification
• Lab Computers
• Start gt Programs gt SPSS for Windows gt SPSS
  11.0 for Windows

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Start Screen

• Dont show this dialog in the future.
• OK

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Open Breast Cancer Survival
Data View
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Views
Variables View
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File Information

• Utilities Menu
• File Info
• Output window

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Descriptive Statistics

• Analyze Menu
• Descriptive Statistics
• Frequencies
• Select Age ?
• Click Statistics button
• In Central Tendency
• Mean, Median, Mode
• In Dispersion
• Standard Deviation, variance

• In Percentile Values
• Quartiles
• Continue
• OK

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Graphing

• Graphs Menu
• Pie
• Summary for Groups of cases
• Lymph Nodes ?
• OK

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Histogram with Normal Curve

• Graphs Menu
• Histogram..
• Select Age ?
• Check Display Normal Curve
• OK

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Simple Correlation Analysis

• Age and Tumor Size
• Analyze Menu
• Correlate
• Bivariate
• Select Age ?
• Select Pathological Tumor Size ?
• Check Pearson and Spearman Two tailed
• OK
• Is there a correlation? Negative or Positive?
• Is it statistically significant?

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Save Output

• Save on All Users drive
• Under Nancy.clark
• SPSS Output Files
• Name it your name ie, KerryBachista.spo

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Importing Data

• From Excel, SAS, dBase, etc.
• Variable names first row
• File Menu, Open
• Data
• Files of Type
• Excel
• Tutorial, Samples
• Demo.exe

• Type in Labels
• Pick Type of variable
• Enter Value Labels
• Etc.

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SPSS Tutorials

• In the Help Menu
• On Informatics Web page
• Books
• Statistics for Social Health Research (Sage)
• Argyrous, George
• Statistics Applied to Clinical Trials (Klawer
  Academic Publishers)
• Cleophas, Ton J., et al

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Objectives

• Determine what data exist relative to a clinical
  question or formal hypothesis
• use IT to locate existing data sources
• identify and locate existing data sets
• Within institution
• Outside institution
• Analyze, interpret and report findings
• Select appropriate computer software Excel, SPSS
• Use software to perform simple statistical
  analysis and portray results graphically
• Interpret reports

51
Questions?