eChapters

One of the objectives of experiments in cultivators’ field is to test technology for adoption in a targeted area i.e. NARP Zone, or a district. In that case interaction between district x treatment within a zone or between blocks x treatment within a district should not be significant. If the targeted area is a district, an experiment in cultivators’ fields must occur in at least two blocks. Also, if the targeted area is a zone, an experiment should occur in at least two districts in order to estimate interaction.

Analysis of cultivators’ field experiment

The on-farm trials were conducted in 25 villages on kharif rice during 1992-93. The treatments viz. T1-Farmers’ practice with local variety, T2-Farmers’ practice with improved variety, T3-Farmers’ practice with improved variety +recommended fertilizer and T4-Improved practice with improved variety +recommended fertilizer. Farmers level of NPK fertilizer was 40:0:0 and local variety was Suzata while recommended NPK fertilizer was 80:40:20.

There are a number of different cell lines derived from human and animals. With the dramatic increase in numbers of cell lines, the risk of intraspecies and interspecies cross contamination rises proportionally. It is particularly a major problem in laboratories where many different cell lines of human and animal origin are handled at a time. The purity of the primary cell or continuous cell lines and species of its origin should be checked on a regular basis to authenticate the cell line identity. In the absence of such monitoring, inter and intra species cell line contamination are likely to occur in the laboratory resulting in loss of investigator’s time effort and resources. The advantages of working with a well defined cell line free from contaminating organisms would appear obvious.

Cell culture contamination continues to be a major problem and a subject of great concern. Contamination may enter the cell culture system as physical, chemical or biological component of the environment and biological contamination represent the greatest threat as living organism metabolize and replicate. Replication increases the titre of the contaminant.
 
Physical contamination : Physical components of cell culture systems such as radiation, irradiation (UV light and fluorescent light), temperature extremes can cause reduced cell growth and cell death. To minimize the problems, incubators should be located where ambient temperature is relatively constant and no vibration (near centrifuge). Media and media components should not be stored in glass door refrigerators, next to radioisotopes, bench tops or outside the refrigerator or in the hood for prolonged period.

The important convincing appealing and easily understood method of presenting the statistical data is the use of diagrams and graphs. Diagram makes the comparison of the data but graphs makes the relationship among the data.

Objective: Aggregated figures for merchandise export in India for eight years are as follows

Enumeration of cells is essential to determine the multiplicity of infection, efficiency of plating and to obtain the specific number of cells for an experiment. The concentration of cells of a suspension can be counted using a haemocytometer. Each chamber is divided into a grid of nine large squares. Each large square is 1mmX1mm (area 1 mm²) and the depth is o.1 mm. The volume of each square is 0.1 mm³ or 10^-4 cm³. Since 1 cm³ is equal to 1 ml, the number of cells per ml of suspension can be obtained by multiply the average count per large square by 10⁴ and reciprocal of dilution factor. Dilution is made in such a way that one large square contain about 20-60 cells. The haemocytometer chambers should be filled by capillary action and cell clump are counted as one cell. A total count does not distinguish between living and dead cells. The number of viable cells can be determined by staining the cells with trypan blue or erythrosine B. In trypan blue staining cells appear as unstained whereas dead cells appear as blue.

After fertilization and zygote formation, in utero development can be divided into two stages, i.e. embryonic and foetal. Embryo period refers to the time between fertilization and the development of organ primordia. During the embryonic period, fast development occurs, and primordia of most organs are established. During the foetal stage, which lasts from the end of the embryonic period until parturition, the body’s systems begin to develop and function.

Cell culture is the most convenient and widely used system for the isolation and propagation of many viruses. Either primary cell culture or established cell lines can be used to isolate the suspected viruses. One can normally get 10-100 virus particles per cell inoculated. Many details of the infection process are controllable to a high degree (including cell density, age, multiplicity of infection (M.O.I.), medium composition, cell type and length and temperature of incubation). Many cell types from different species can be susceptible to a particular virus and vice versa. For replication to occur, the cell type used must be permissive for a particular virus under study.

Measures of Central Tendency

The term ‘Mean” or ‘average’ is something, we have been familiar with from a very early age when we start analyzing our marks on report card. We add together all of our test results and then divide it by the sum of the total number of marks there are. We often call it the average. However, statistically it’s the Mean!

The Median is the ‘middle value’. When the totals of the list are odd, the me- dian is the middle entry in the list after sorting the list into increasing order. When the totals of the list are even, the median is equal to the sum of the two middle (after sorting the list into increasing order) numbers divided by two. Thus, remember to line up values, the middle number is the median!

The Mode in a list of numbers refers to the list of numbers that occur most frequently. A trick to remember this one is to remember that mode starts with the same first two letters that most does. Most frequently - Mode.

The most important property of a virus is its infectivity or ability to invade a cell and parasitize that cell to replicate itself. To measure infectivity, a titre is defined as the given number of infectious virus units/unit volume and an infectious unit is the smallest amount of virus that produces some recognizable effect in the host system. There are two basic types of infectivity assays (a) Quantal assays and (b) Quantitative assays.

Quantal assays do not measure the number of infectious virus particles present in the inoculum but denote a value for the virus titre where measurement is based on an all or none principle, CPE + or -, dead or alive etc. In the quantitative assays, the number of virus particles present in the suspension can be quantified.

A relative measure of dispersion based on the quartile deviation is called the coefficient of quartile deviation. It is defined as

MEAN DEVIATION

The mean deviation is the first measure of dispersion that we will use that ac- tually uses each data value in its computation. It is the mean of the distances between each value and the mean. It gives us an idea of how spread out from the center the set of values is.

The mean deviation is based on all the observations, a property which is not possessed by the range and the quartile deviation. The formula of the mean de- viation gives a mathematical impression that is a better way of measuring the variation in the data. Any suitable average among the mean, median or mode can be used in its calculation but the value of the mean deviation is minimum if the deviations are taken from the median.

COEFFICIENT OF THE MEAN DEVIATION

A relative measure of dispersion based on the mean deviation is called the coefficient of the mean deviation or the coefficient of dispersion. It is defined as the ratio of the mean deviation to the average used in the calculation of the mean deviation.

STANDARD DEVIATION AND THEIR COEFFICIENT

The standard deviation is a measure of the spread of scores within a set of data. Usually, we are interested in the standard deviation of a population. However, as we are often presented with data from a sample only, we can estimate the population standard deviation from a sample standard deviation. These two standard deviations - sample and population standard deviations - are calculat- ed differently. In statistics, we are usually presented with having to calculate sample standard deviations.

Precautions to be taken while working in the laboratory for personal safety and to prevent any hazards.
    1.    Be vaccinated against dangerous viruses viz., rabies and hepatitis B as persons can contract infection while working with these organisms.
    2.    Use eye protection viz., goggles, spectacles etc to avoid splashing microbes into the eyes. 
    3.    Do not rub eyes with contaminated hands or objects.
    4.    Do not eat or drink anything in the microbiology laboratory as it will contaminate the laboratory.

FOR GROUPED DATA

Objective: The following data shows the marks of students and their frequencies find the standard deviation and its coefficient.

COEFFICIENT OF VARIATION:

The most important of all the relative measure of dispersion is the coefficient of variation. This word is variation not variance. There is no such thing as coefficient of variance. The coefficient of variation( C.V.) is defined

7.1 Introduction

The theory of probability has its origin in the games of chance related to gambling such as throwing a die, tossing a coin, drawing cards from a pack of cards etc. Jerame Cardon (1501-1576), an Italian mathematician was the first man to write a book on the subject entitled “Book on Games and Chance”, which was published after his death in 1663. The systematic and scientific foundation of the mathematical theory of probability was laid in mid-seventeenth century by two French mathematicians B. Pascal (1623-1662) and Pierre de Fermat (1601-1665).

CORRELATION

In case of bivariate or multivariate normal distributions, we may be interested in discovering and measuring the magnitude and direction of the relationship between two or more variables. For this purpose we use correlation. The sys- tematic interrelationship between the variables is termed as correlation. When only two variables are involved the correlation is known as simple correlation. If more than two variables are involved the correlation is known as multiple correlation. An increase in one variable may cause an increase in the other variable, or a decrease in one variable may cause a decrease in the other vari- able, then they are said to be positively correlated. If a decrease in one variable causes an increase in the other variable or vise versa, the variables are said to be negatively correlated.

TEST OF SIGNIFICANCE FOR CORRELATION COEFFICIENT

Coefficient of correlation is a numeric characteristic of a population and is estimated from a sample of the bi-variate population. If ρ be the coefficient of correlation in the population and r be its sample estimate based on n pairs of observations, then standard error of r is given

t TEST FOR SINGLE MEAN

A t-test is any statistical hypothesis test in which the test statistic follows a Student’s t distribution if the null hypothesis is supported. It can be used to determine if two sets of data are significantly different from each other, and is most commonly applied when the test statistic would follow a normal distribution if the value of a scaling term in the test statistic were known. When the scaling term is unknown and is replaced by an estimate based on the data, the test statistic (under certain conditions) follows a Student’s t distribution.