8/9/2019 Basic Biostat
1/27
Basics of Biostatistics
Dr Sumanth MM
Assistant Professor, Community Medicine, MMCRI, MysoreMBBS,MD,DNB
8/9/2019 Basic Biostat
2/27
Constant and variable
A constant is a quantity which within the framework of a given problem, remains unchanged;
A variable takes on various values.
The same quantity may be a constant in somesituation and a variable in another.
Types of variable
- Continuous - Quantitative- Discrete - Qualitative
- Random
8/9/2019 Basic Biostat
3/27
Scales of measurements
Nominal
Ordinal
Interval
Ratio
8/9/2019 Basic Biostat
4/27
- Independent - ( Intervening ) - Dependent
- Cause - ( Confounding) - Effect
- Input - ( Process ) - Output
- Predicting - ( Disturbing ) - Predicted
- Experimental - ( Random ) - Outcome
Variables at different settings
8/9/2019 Basic Biostat
5/27
Data Analyses/Syntheses Process
Screening /Verification/Cleaning up
Organization
Compilation /Collation &
Classification (Nominal/Ordinal/Numerical)
Grouped Frequency Distribution
Tabulation
Graphical representations
8/9/2019 Basic Biostat
6/27
Summary Statistics
Rates, Ratios and Proportions
Incidence & Prevalence (Point /Period)
Numerator and Denominator
Per Cent / Thousand / Lakh / Million
8/9/2019 Basic Biostat
7/27
Summary Statistics
Measures of
Central Tendency averages
Dispersion/Deviation
/Scatter/Variation/ Spread
Locationpercentiles /quintiles
8/9/2019 Basic Biostat
8/27
Measures of Central Tendency
Mean (Simple / Arithmetic)
Median
Mode
Weighted Mean (average of average or of percentages)t
8/9/2019 Basic Biostat
9/27
Measures of Dispersion
Range (min. - max.)
Modified Range
Average Deviation (from Mean/given point)
Variance
Standard Deviation
Coefficient of Variation (CV expressed in relative %)
8/9/2019 Basic Biostat
10/27
Measures of Location
Percentiles (100thfraction/partition)
Deciles (10thfraction/partition)
Quartiles (25thpercentile)
Median (50thpercentile or 5thdeciles)
Inter - Quartile range (Q3 Q1)
Inter - Deciles range (D9 D1)
8/9/2019 Basic Biostat
11/27
Mean3 2 +2 +3
95.5%
99.7%
The role of Central tendency
and Deviation
8/9/2019 Basic Biostat
12/27
8/9/2019 Basic Biostat
13/27
8/9/2019 Basic Biostat
14/27
Data entry and analysis
8/9/2019 Basic Biostat
15/27
Objectives
You should be able to make master chart
You should be able to understand the guidelines
to enter data
8/9/2019 Basic Biostat
16/27
Always make it soft copy
Follow data sheet/questionnaire for data entry
Use excel/spss/graphpad Identification for each observation is essential
8/9/2019 Basic Biostat
17/27
Always know questionnaire
Always enter data uniformly
(capital letter etc)
Codes to be used
Column title should be simple, logical easy tounderstand
Units need not be entered
Dont change the variable type (keep continuousvariables as it is)
8/9/2019 Basic Biostat
18/27
8/9/2019 Basic Biostat
19/27
Prepare master chart for your topic in excel
8/9/2019 Basic Biostat
20/27
Data analysis
Data ---- information
Summary
Mean, Median, ModeRange, IQR, SIQR, Variablity
Proportion, OR, RR, Mean difference, Difference ofProportion
Inferential SEP, SEM, SEDP, SEDM Identifies role of chance
8/9/2019 Basic Biostat
21/27
8/9/2019 Basic Biostat
22/27
Group A- SEM-3 mean 10, 7-13
Group B- SEM-1 mean 9, 8-10
Identify role of chance
Statistical tests/ tests of significance
8/9/2019 Basic Biostat
23/27
Prarametric tests
Non-parametric tests
Where do you which tests?
T p f D t
8/9/2019 Basic Biostat
24/27
Type of Data
Goal Measurement (from
Gaussian Population)
Rank, Score, or Measurement
(from Non- Gaussian
Population)
Binomial
(Two Possible
Outcomes)
Describe one group Mean, SD Median, interquartile range Proportion
Compare one group to a
hypothetical value
One-sample ttest Wilcoxon test Chi-square
or
Binomial test **
Compare two unpairedgroups Unpaired ttest Mann-Whitney test Fisher's test
(chi-square for large
samples)
Compare two paired groups Paired ttest Wilcoxon test McNemar's test
Compare three or more
unmatched groups
One-way ANOVA Kruskal-Wallis test Chi-square test
Compare three or more matched
groups
Repeated-measures ANOVA Friedman test Cochrane Q**
Quantify association between
two variables
Pearson correlation Spearman correlation Contingency
coefficients**
Predict value from another
measured variable
Simple linear regression
or
Nonlinear regression
Nonparametric regression** Simple logistic
regression*
Predict value from several
measured or binomial variables
Multiple linear regression*
or
Multiple nonlinear regression**
Multiple logistic
regression*
8/9/2019 Basic Biostat
25/27
Test depends on
Study design
Type of variable
8/9/2019 Basic Biostat
26/27
softwares
SPSS
GRAPH PAD
SYSSTATSTATA
SAS
Epi info
8/9/2019 Basic Biostat
27/27