Dr. Mona Hassan Ahmed Hassan Prof. Biostatistics

for Diabetes Epidemiology Computer Utilization for Diabetes Epidemiology

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

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

Data Preparation Ser. Ser. Column Code Age Sex MS Educ. Coding form Either the information is transferred from the original record to a “coding sheet” Ser. Ser.  Column Code Age Sex MS Educ. Coding form

Code 1 10/01/2008 25/08/1986 ID 1 1. Date of Interview 10/1/2008 f 160 58 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. 

Scales of measurement

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

Scales of Measurement

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 variables  chi-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 1 SAS 2 SPSS 3 STATA 4 Epi Info 5 SUDAAN 6 S-PLUS 7 MedCalc 8 Excel 9 Statistica 10 Minitab Sample size

Using Epitable (Under EpiInfo) to Calculate 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 entry

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

Simple frequency Data check

Perform Descriptive Statistics

Descriptive

Conduct Simple Correlations and regression

Correlation

Regression

Scatter

t- test (Two independent groups)

t- test (Two independent groups)

t- test (Two independent groups)

Paired t- test (Dependent groups)

Chi-Square test

Thank You