Dr. Mona Hassan Ahmed Hassan

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• Dr. Mona Hassan Ahmed Hassan
• Prof. Biostatistics

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Computer Utilization
for Diabetes Epidemiology
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Statistical Software
What to do before sitting to PC?
How to generate and interpret results?
Objectives
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Data Coding

• Transformation of qualitative information into
• Numbers
• OR
• Symbols

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Data Preparation
Either the information is transferred from the
original record to a coding sheet
Ser. Ser. Ser. Ser. Ser.  Ser. 
Column Code Column Code Column Code
Age Age Age
Sex Sex Sex
MS MS MS
Educ.
Coding form
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Code
1
10/01/2008
25/08/1986

f
1

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

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Coding by more than one person

• Precise instructions should be developed for
  coders
• Coders, must be trained
• check for inter-coder reliability

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

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Scales of measurement
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Scales of Measurement
Ali
Ramy
Samy
Nominal Symbols Assigned to
Runners Ordinal Rank Order of
Winners Interval Performance Rating on a
0 to 10 Scale Ratio Time to Finish, in
Seconds

Finish
Finish
3
7
9
15.2
14.1
13.4
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Scales of Measurement
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Shapes of Distribution
Mean Median Mode
68 within meanSD 95 within mean2SD 99 within
mean3SD
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Right-skewed distribution
Mode Median Mean

• If Mean gt Median ? Positive or right skewness
• 
  (long right tail)
• It arises when the mean is increased by some
  unusually high values

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Left-skewed distribution
Mean Median Mode

• If Mean lt Median ? Negative or left skewness
  (long left tail).
• Negative skewness occurs when the mean is reduced
  by some extremely low values.

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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

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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
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Using Epitable (Under EpiInfo) to Calculate
Sample Size
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SPSS
Statistical
Sciences
Packages
Social
FOR
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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

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Data Entry

• Excel
• Access
• Word
• Any Statistical software

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Data entry
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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

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Simple frequencyData check
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• Perform Descriptive Statistics

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Descriptive
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Conduct Simple Correlations and regression
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Correlation

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Regression

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Scatter
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t- test (Two independent groups)
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t- test (Two independent groups)
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t- test (Two independent groups)
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Paired t- test (Dependent groups)
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Chi-Square test
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Thank You