Research Perspective
Nancy B. Clark. M.Ed.
Director of Medical Informatics Education
FSU College of Medicine
Spring 2004 http://www.med.fsu.edu/informatics

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

Prerequisite Skills
(Step 1 USMLE)
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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

More Prerequisite Skills
(Step 1 USMLE)
 Fundamental concepts of hypothesis testing and statistical inference
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Confidence intervals
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Statistical significance and type I error
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Statistical power and type II error

More Step 1 Topics
 Fundamental concepts of study design
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Types of experimental studies (eg, clinical trials, community intervention trials)
Types of observational studies (eg, cohort, casecontrol, 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

Scales of Measure
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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

Distribution, Central Tendency…
Mean

…Variability, Probability…
 Mean
 Median
 Mode
 Standard deviation
 Statistical Significance p < .01

Confidence Interval

Statistical Significance
Type I and Type II errors
Null Hypothesis = H o
H o
True H o
False
Reject H o
Type I error Correct decision
Do Not Reject H o
Correct decision Type II error

Statistics Online Textbook
 The Statistics Homepage
 http://www.statsoftinc.com/textbook/stathome
.html

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

Sensitivity, Specificity
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 sensitivity = a / (a+c) specificity = d / (b+d)
Test is positive
Test is negative
Patients with disease
Patients without disease a c b d

Predictive Value
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Positive predictive value = a / ( a+b)
Negative predictive value = d / (c+d)
Post-test probability of disease given positive test = a / (a+b)
Test is positive
Post-test probability of disease given negative test = c / (c+d)
Test is negative
Patients with disease
Patients without disease a b c d

Good Resource Sen, Spc, PV
 An Introduction to Information Mastery
 http://www.poems.msu.edu/InfoMastery/defa ult.htm

Diagnosis
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Sensitivity and specificity
Predictive values
 Likelihood ratios
 InfoRetriever
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Calculators: Epidemiology, Diagnostic test

Fundamental Concepts of Study Design
 Good Resource
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Epidemiology for the Uninitiated
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BMJ
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Online Textbook
 http://bmj.com/collections/epidem/epid.shtml

Types of Health Statistics Questions
 Fact lookups
 Research
 Presentations
 Social and Policy indicators

Strategies for Finding Health Stats
 Use Portal
 Start at Internet site
 Start with book or article

Internet Portals of Health Stats
 Lists of links that provide starting points for browsing or searching

Keyword search in portal vs Google
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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/

Other Statistical Web Sites
 CDC Data and Statistics http://www.cdc.gov/scientific.htm
 FedStats Home Page http://www.fedstats.gov/
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Compare these two
U Michigan’s Statistical Resources on the
WEB – HEALTH
 What type of stats

Lexis-Nexis Statistical Universe
 Subscription resource
 Searches stat data
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Subject List
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Limit search
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Reports or tables
 http://web.lexisnexis.com/statuniv?B1=Connect+to+Statistic al+Universe

MMWR
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Morbidity – illness
Mortality – death
 http://www.cdc.gov/mmwr/
 Disease Trends
 Tables - searchable

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

Health Consequences
 Costs to society, individuals
 Cost from care
 Costs of illness
 Impact on infrastructure
 HCFA=>CMS Health Accounts
 http://www.cms.hhs.gov/statistics/nhe/default.
asp

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

Individual Datasets
 EMR
 Billing
 CDCS
 Customized data collection tools

Selecting the Appropriate Software
 Spreadsheet
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Numerical (interval or ratio) data
Sums
Averages
Standard deviations
Simple charts and graphs
 Statistical Software
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Nominal or Ordinal data
Comparisons of two+ groups
Frequency tables
Complicated charts and graphs
Normal curves
Class intervals
Statistical significance

Spreadsheets
 Excel
 Pocket Excel

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

Descriptive Statistics
 Distribution
 frequency distribution
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Histogram
 Central tendency
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Mean
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Median
 mode
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Dispersion
 Range
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Standard deviation
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Variance
N
Not P (inferential stats)

Central Tendency
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Mean
 =AVERAGE(b2:b1500)
Median
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=MEDIAN(A2:A7)
Mode
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=MODE(A2:A7)
N
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=COUNT(A2:A1500)
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=COUNTBLANK(A2:B5)

Dispersion
 Range
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=MAX(A2:A60)- MIN(A2:A60)
 Standard deviation
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=STDEV(A2:A110)
 Variance
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=VAR(A2:A110)

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

Hands on experience
 Analyze data in examples2.xls

Statistical Software
 SPSS
 Provided by request/justification
 Lab Computers
 Start => Programs => SPSS for Windows =>
SPSS 11.0 for Windows

Start Screen
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Don’t show this dialog in the future.
OK

Open Breast Cancer Survival
Data View

Views
Variables
View

File Information
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Utilities Menu
File Info…
Output window

Descriptive Statistics
 Analyze Menu
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Descriptive Statistics
Frequencies
Select Age ►
Click Statistic s button
In Central Tendency
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Mean, Median, Mode
 In Dispersion
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Standard Deviation, variance
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In Percentile Values
 Quartiles
Continue
OK

Graphing
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Graphs Menu
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Pie…
Summary for Groups of cases
Lymph Nodes ►
OK

Histogram with Normal Curve
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Graphs Menu
 Histogram..
Select Age ►
Check Display Normal
Curve
OK

Simple Correlation Analysis
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Age and Tumor Size
Analyze Menu
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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?

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

Importing Data
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From Excel, SAS, dBase, etc.
Variable names first row
File Menu, Open
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Data…
Files of Type
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Excel
 Tutorial, Samples
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Demo.exe
 Type in Labels
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Pick Type of variable
Enter Value Labels
Etc.

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

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