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Dr. Mona Hassan Ahmed Hassan Prof. Biostatistics PowerPoint Presentation
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Dr. Mona Hassan Ahmed Hassan Prof. Biostatistics - PowerPoint PPT Presentation

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Dr. Mona Hassan Ahmed Hassan Prof. Biostatistics

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  1. Dr. Mona Hassan Ahmed Hassan Prof. Biostatistics

  2. Computer Utilization for Diabetes Epidemiology

  3. Statistical Software What to do before sitting to PC? How to generate and interpret results? Objectives

  4. Data Coding Transformation of qualitative information into Numbers OR Symbols

  5. Data Preparation Either the information is transferred from the original record to a “coding sheet” Coding form

  6. ID 1 1. Date of Interview 10/1/2008 2. What is your date of Birth? 25/8/1986 3. What sex are you? Male (m) Female (f) 4. What is your marital status? Single (1) Married (2) Widowed (3) Divorced (4) 5. What is your height (cm)?160 6. What is your weight (kg)?58

  7. Coding by more than one person • Precise instructions should be developed for coders • Coders, must be trained • check for inter-coder reliability

  8. Sorting of the questionnaires 101-200 1-100

  9. Describing the Sample • measures of central tendency and variability.  • The appropriate measure of central tendency and variability will depend upon the variables level of measurement and the shape of the distribution. 

  10. Scales of measurement

  11. 3rd place 2nd place 1st place Scales of Measurement Ali Samy Ramy Nominal Symbols Assigned to Runners Ordinal Rank Order of Winners IntervalPerformance Rating on a 0 to 10 Scale Ratio Time to Finish, in Seconds Finish Finish 3 7 9 15.2 14.1 13.4

  12. Scales of Measurement

  13. Shapes of Distribution Mean Median Mode • 68% within mean+SD • 95% within mean+2SD • 99% within mean+3SD

  14. Right-skewed distribution Mode Median Mean If Mean > Median  Positive or right skewness (long right tail) It arises when the mean is increased by some unusually high values

  15. Left-skewed distribution Mean Median Mode If Mean < Median  Negative or left skewness (long left tail). Negative skewness occurs when the mean is reduced by some extremely low values.

  16. Inference Developing and Testing a Hypothesis differences in frequency distributions of nominal level variableschi-square associations or correlations between variables,  bivariate correlations differences between groups with respect to the distribution of interval/ratio level data.t-tests

  17. The most popular statistical packages Sample size

  18. Using Epitable (Under EpiInfo) to Calculate Sample Size

  19. SPSS Statistical Sciences Packages Social FOR

  20. Creating a Data File in SPSS • ID • Gender Male Female • Date of Birth • Educational Level (years) • Employment Category 1 Clerical 2 Custodial 3 Manager • Current Salary $ • Beginning Salary $ • Months since Hire • Previous Experience (months) • Minority Classification 0 No 1 Yes

  21. Data Entry Excel Access Word Any Statistical software

  22. Data entry

  23. Data cleaning • General data check: Printout • Quick data check (Frequency tables) 1- Wild codes check (invalid codes) 2- Completeness check:ensure that all cases collected are represented in the data file without replication

  24. Simple frequencyData check

  25. Perform Descriptive Statistics

  26. Descriptive

  27. Conduct Simple Correlations and regression

  28. Correlation

  29. Regression

  30. Scatter

  31. t- test (Two independent groups)

  32. t- test (Two independent groups)

  33. t- test (Two independent groups)

  34. Paired t- test (Dependent groups)

  35. Chi-Square test

  36. Thank You