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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. 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

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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. 


Scales of measurement


3rd place

2nd place

1st place

Scales of Measurement

Ali

Samy

Ramy

Nominal Symbols

Assigned

to Runners

OrdinalRank Order

of Winners

IntervalPerformance

Rating on a

0 to 10 Scale

RatioTime to Finish, in

Seconds

Finish

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 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


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 Classification0 No1 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 frequencyData 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


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