# Statistical Data / Variables – Introduction (Classification of Statistical Data / Variable – Numeric vs Categorical)

## What is ‘data’ or ‘variable’?

Ø  Data is a set of values of qualitative or quantitative variables.

Ø  In biostatistics (also in statistics) data are the individual observations.

Ø  The scientific investigations involve observations on variables.

Ø  The observations made on these variables are obtained in the form of ‘data’.

Ø  Variable is a quantity or characteristic which can ‘vary from one individual to another’.

Ø  Example: Consider the characteristic ‘weight’ of individuals and let it be denoted by the letter ‘N’. The value of ‘N’ varies from one individual to another and thus, ‘N’ is a variable.

Ø  Data and variable are not exact but used frequently as synonyms.

Ø  The variables can also be called as ‘data items’.

Ø  Majority of the statistical analysis are done on variables.

### Type of Variables in Statistics

Statistical variables can be classified based on two criterion (I) Nature of Variables and (II) Source of variables

I. Classification of variable based on Nature of Variables

Ø  Based on the nature of variables, statistical variables can be classified to TWO major categories such as (1) Numerical and (2) Categorical.

# Biostatistics – Introduction (Significance, Applications and Limitations of Biostatistics)

## What is Statistics?

Statistics is a branch of applied mathematics which deals with the collection, classification, analysis and interpretation of data. The word statistics is derived from the Latin word ‘status’ means a ‘political state’ or ‘government’.

### What is Biostatistics?

Biostatistics is a branch of biological science which deals with the study and methods of collection, presentation, analysis and interpretation of data of biological research. Biostatistics is also called as biometrics since it involves many measurements and calculations. In biostatistics, the statistical methods are applied to solve biological problems. Basic understanding of biostatistics is necessary for the study of biology particularly doing research in biological science. The statistics will help the biologist to: (1) understand the nature of variability and (2) helps in deriving general laws from small samples.

# Phase Contrast Microscopy PPT

What is Phase Contrast Microscope? What are the limitations of ordinary light microscope? Who invented the phase contrast microscope? What is the working principle of phase contrast microscope? What are the optical components of phase contrast microscope? What is the importance of Annular Diaphragm and Phase Plate in phase contrast microscope? How contrast is created in phase contrast microscopy? What are the applications of phase contrast microscope? What are the limitations of phase contrast microscopy?

# Phase Contrast Microscopy (Optical Components, Working Principle and Applications of Phase Contrast Microscope)

Working Principle of an Ordinary Microscope:

In an ordinary microscope, the object is viewed due to differences in colour intensities of the specimen. To create the colour intensities, the specimen is first stained with suitable dyes which will impart specific colour. In an ordinary microscope, the contrast is obtained when the light rays pass through a stained specimen because different stains absorb different amounts of light. These differential absorption properties of stained specimen modify the intensity or amplitude of the light waves transmitted by different regions of the cells and this ultimately creates contrast in the image. Thus, staining is essential to create contrast in an ordinary microscope. Moreover, the unstained specimen cannot be observed through an ordinary microscope.

Why Phase Contrast Microscope?

The Phase Contrast Microscope is used to visualize unstained living cells. Most of the stains or staining procedures will kill the cells.  Phase contrast microscopy enables the visualization of living cells and life events.

# Titration Curve of a Weak Acid and its pKa (Titration, Titration Curve, Titration Curve of Acetic Acid and its Significance)

## What is Titration?

Titration is a method to determine the concentration of a dissolved substance (analyte or titrand) in a known volume by reacting it with another substance of known concentration and volume (titrant). The volume of the reactants plays a crucial role in the titration and thus the titration is better called as ‘volumetric analysis’.

There are different types of titrations in which the Acid-Base Titration is the most common one. The acid-base titration is used to determine the amount (concentration) of an acid in a given solution. In an acid-base titration, a known volume of acid (of unknown concentration) is titrated against a solution of strong base (usually NaOH) of known concentration in the presence of an indicator. After the titration, the concentration of the acid in the sample is calculated using the concept N1V1 = N2V2.

Where,

N1 – Normality of the unknown acid

N2 – Normality of the known base

V1 – Volume of unknown acid

V2 – Volume of the known base

### What is Titration Curve?

The titration curve is a graphical representation of a titration in which the volume of titrant is plotted on X-axis (as the independent variable) and the pH of the solution is plotted on the Y-axis (as the dependent variable).

In simple terms, the titration curve is the plot of pH of the analyte (titrand) versus the volume of the titrant added as the titration progresses.