This document provides an overview of key concepts for analyzing medical data from a research perspective, including: - Statistical concepts important for medical licensing exams like scales of measurement, distributions, hypothesis testing, and study designs. - How to determine what data is available to answer a clinical question, locate existing datasets, and analyze/interpret findings using software like Excel and SPSS. - Resources for further learning about epidemiology, health statistics, diagnostic tests, and using statistical software.

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

2. 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

4. 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

5. 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

6. 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

7. Distribution, Central Tendency… Mean

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

9. Confidence Interval

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

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

12. 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

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

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

15. 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

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

17. Finding Health Statistics

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

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

20. 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/

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

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

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

24. 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

25. 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

26. 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

27. Individual Datasets EMR Billing CDCS Customized data collection tools

28. Data Analysis

29. 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

30. Spreadsheets Excel Pocket Excel

31. 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

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

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

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

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

36. Hands on experience Analyze data in examples2.xls

37. Statistical Software Intro to SPSS

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

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

40. Open Breast Cancer Survival Data View

41. Views Variables View

42. File Information Utilities Menu File Info… Output window

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

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

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

46. 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?

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

48. 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.

49. 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

50. 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?