Lecture 4

Clinical epidemiology. Modern principles and rules conducting of

clinical researches. Concept of null hypothesis

The term null hypothesis was coined by the English geneticist and statistician Ronald Fisher.

Null hypothesis

Null hypothesis (H0) is a hypothesis (scenario) set up to be nullified, refuted, or rejected ('disproved' statistically) in order to support an alternative hypothesis. When used, the null hypothesis is presumed true until statistical evidence, in the form of a hypothesis test, indicates otherwise — that is, when the researcher has a certain degree of confidence, usually 95% to 99%, that the data does not support the null hypothesis. It is possible for an experiment to fail to reject the null hypothesis. It is also possible that both the null hypothesis and the alternate hypothesis are rejected if there are more than those two possibilities.

Null hypothesis

Null hypothesis

Let’s return to the question of whether we

(a) reject or accept the null hypothesis; and

(b) if we reject the null hypothesis, do we accept the alternative hypothesis.

Four primary types of epidemiology studies

If our statistical analysis shows that the two distributions are the same at the significance level (either 0.05 or 0.01) that we have set, we simply accept the null hypothesis.

Alternatively, if the two distributions are different, we need to either accept or reject the alternative hypothesis. This will depend on whether we made a one- or two-tailed prediction.

Randomization is the process of making something random; this means:

Generating a random permutation of a sequence (such as when shuffling cards).

Selecting a random sample of a population (important in statistical sampling).

Generating random numbers: see Random number generation.

Transforming a data stream using a scrambler in telecommunications.

Randomization

Randomization is used extensively in the field of gambling (or generally being random). Imperfect randomization may allow a skilled gambler to have an advantage, so much research has been devoted to effective randomization. A classic example of randomization is shuffling playing cards.

Other uses of randomization

Randomization is a core principle in the statistical theory of design of experiments. Its use was extensively promoted by R.A. Fisher in his book Statistical Methods for Research Workers. Randomization involves randomly allocating the experimental units across the treatment groups. Thus, if the experiment compares a new drug against a standard drug used as a control, the patients should be allocated to new drug or control by a random process.

Other uses of randomization

Although historically "manual" randomization techniques (such as shuffling cards, drawing pieces of paper from a bag, spinning a roulette wheel) were common, nowadays automated techniques are mostly used. As both selecting random samples and random permutations can be reduced to simply selecting random numbers, random number generation methods are now most commonly used, both hardware random number generators and pseudo-random number generators.

Randomization Techniques

Stratification is the building up of layers, and can have several meanings

Social stratification, is the dividing of a society into levels based on wealth or power.

Stratification in archaeology is the formation of layers (strata) in which objects are found.

Stratification of rock layers (strata) is part of the geologic field of Stratigraphy.

Stratification

  Total Male Female

Scotland (1983) 192.3 283.9 124.0

Finland (1980) 176.5 283.7 101.7

Sweden (1982) 158.4 231.5 98.0

Australia (1981) 155.9 223.7 100.3

England &Wales (1982) 154.7 231.4 94.9

USA (1980) 154.6 219.7 104.1

Denmark (1982) 153.4 220.6 99.6

Canada (1982) 145.1 205.2 94.7

Italy (1980) 79.6 113.8 51.9

France (1981) 47.3 71.5 28.1

Japan (1982) 29.5 39.3 22.0

Age standardized death rate of CHD per 100,000 population in selected countries

Stratification (botany), where seeds are pretreated to simulate winter conditions so that germination may occur.

In logic, stratification is a layering of predicate symbols to guarantee unique interpretations and to avoid paradoxical definitions like Russell's paradox.

In mathematics, Stratification has a separate meaning as applied to manifolds, and singularity theory, of a decomposition into pieces with specified relationships on fitting together.

Stratification

In music stratification is a layering of musical texture or the independent operating of more than one parameter simultaneously (see auditory stream).

In meteorology, atmospheric stratification is the division of the atmosphere into distinct layers, each with specific properties such as temperature or humidity.

In histology, stratified epithelium refers to epithelium that consists of two or more layers of epithelial cells, in contrast to simple epithelium, which only has one layer.

Stratification

It is an internationally recognised structure which enables those working to improve the health of local communities and apply Health for All principles, to meet and share information, research and experiences.

The Network was established in 1987. It currently receives a grant from the Department of Health (England).

In 1995 the Network became a Company Limited by Guarantee in order to affiliate formally to the World Health Organisation and other networks. In 1997 the Network became a registered UK charity.

“HEALTH FOR ALL”