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(Basic Statistical Knowledge)Yararlı olmasını dileriz..Sevgi ve saygı ile.
29 Eylül 2014, AnkaraDr. Ahmet SALTIK
www.ahmetsaltik.net**************Şöyle giriyoruz… (Introduction)
BRIEF STATISTICAL NOTES
(Basic Statistical Knowledge)
Dr. Ahmet SALTIK
AÜTF Halk Sağlığı AbD, June 2005
- Statisticians define a population as the entire collection of items that is the focus of concern. The branch of Statistics called Descriptive Statistics, provides us with ways to describe the characteristics of a given population by measuring each of its items and then summarizing the set of measures in various ways.
- The branch of Statistics called Inferential Statistics consists of procedures to make educated inferences about the characteristics of a population by drawing a random sample and appropriately analyzing the information it provides.
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Devamla… (Going through..)
- A statistical test is a procedure for deciding whether an assertion (e.g.
an Hypothesis) about a quantitative feature of a population is true or false.
We test an hypothesis of this sort by drawing a random sample from the population in question and calculating an appropriate statistic on its items.
If, in doing so, we obtain a value of the statistic that would occur rarely when the hypothesis is true, we would have reason to reject the hypothesis. With this procedure it is customary to reject the hypothesis tested when our statistic has a value that is among those that, theoretically, would be expected to occur no more than 5 out of every 100 times that a random sample (of the same size) is drawn from the population in question when the hypothesis is, in fact, true. Much of the text of this tutorial is devoted to explanations of exactly how this kind of theoretical expectation is developed. - Finally, it is noteworthy that the appropriate conduct of any statistical test invariably requires many thoughtful decisions. It is, for example, always necessary to decide what statistic to use, what sample size to employ and what criteria to establish for rejection of the hypothesis tested.
- The null hypothesis is a term that statisticians often use to indicate the statistical hypothesis tested. The purpose of most statistical tests, is to determine if the obtained results provide a reason to reject the hypothesis that they are merely a product of chance factors. For example, in an experiment in which two groups of randomly selected subjects have received different treatments and have yielded different means, it is always necessary to ask if the difference between the obtained means is among the differences that would be expected to occur by chance whenever two groups are randomly selected. In this example, the hypothesis tested is that the two samples are from populations with the same mean. Another way to say this is to assert that the investigator tests the null hypothesis that the difference between the means of the populations from which the samples were drawn, is zero. If the difference between the means of the samples is among those that would occur rarely by chance when the null hypothesis is true, the null hypothesis is rejected and the investigator describes the results as statistically significant.
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Ve bağlıyoruz… (Finally)
Transformation rule (1) : Adding a constant to every item in a distribution adds the constant to the mean of the distribution, but it leaves the variance and standard deviation, unchanged.
Transformation rule (2) : Multiplying every item in a distribution by a constant multiplies the mean and standard deviation of that distribution by the constant and it multiplies the variance of the distribution by the square of the constant.
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