Basic Biostat

8/9/2019 Basic Biostat

1/27

Basics of Biostatistics

Dr Sumanth MM

Assistant Professor, Community Medicine, MMCRI, MysoreMBBS,MD,DNB


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


3/27

Scales of measurements

Nominal

Ordinal

Interval

Ratio


4/27

- Independent - ( Intervening ) - Dependent

- Cause - ( Confounding) - Effect

- Input - ( Process ) - Output

- Predicting - ( Disturbing ) - Predicted

- Experimental - ( Random ) - Outcome

Variables at different settings


5/27

Data Analyses/Syntheses Process

Screening /Verification/Cleaning up

Organization

Compilation /Collation &

Classification (Nominal/Ordinal/Numerical)

Grouped Frequency Distribution

Tabulation

Graphical representations


6/27

Summary Statistics

Rates, Ratios and Proportions

Incidence & Prevalence (Point /Period)

Numerator and Denominator

Per Cent / Thousand / Lakh / Million


7/27

Summary Statistics

Measures of

Central Tendency averages

Dispersion/Deviation

/Scatter/Variation/ Spread

Locationpercentiles /quintiles


8/27

Measures of Central Tendency

Mean (Simple / Arithmetic)

Median

Mode

Weighted Mean (average of average or of percentages)t


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 %)


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)


11/27

Mean3 2 +2 +3

95.5%

99.7%

The role of Central tendency

and Deviation


12/27


13/27


14/27

Data entry and analysis


15/27

Objectives

You should be able to make master chart

You should be able to understand the guidelines

to enter data


16/27

Always make it soft copy

Follow data sheet/questionnaire for data entry

Use excel/spss/graphpad Identification for each observation is essential


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)


18/27


19/27

Prepare master chart for your topic in excel


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


21/27


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


23/27

Prarametric tests

Non-parametric tests

Where do you which tests?

T p f D t


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*


25/27

Test depends on

Study design

Type of variable


26/27

softwares

SPSS

GRAPH PAD

SYSSTATSTATA

SAS

Epi info


27/27

Documents

Basic Biostat