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Dr. Mona Hassan Ahmed Hassan Prof. Biostatistics. Computer Utilization . for Diabetes Epidemiology. Statistical Software . What to do before sitting to PC?. How to generate and interpret results?. Objectives. Data Coding. Transformation of qualitative information into Numbers OR
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Dr. Mona Hassan Ahmed Hassan Prof. Biostatistics
Computer Utilization for Diabetes Epidemiology
Statistical Software What to do before sitting to PC? How to generate and interpret results? Objectives
Data Coding Transformation of qualitative information into Numbers OR Symbols
Data Preparation Either the information is transferred from the original record to a “coding sheet” Coding form
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
Coding by more than one person • Precise instructions should be developed for coders • Coders, must be trained • check for inter-coder reliability
Sorting of the questionnaires 101-200 1-100
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.
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
Shapes of Distribution Mean Median Mode • 68% within mean+SD • 95% within mean+2SD • 99% within mean+3SD
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
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.
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
The most popular statistical packages Sample size
SPSS Statistical Sciences Packages Social FOR
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
Data Entry Excel Access Word Any Statistical software
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