duanguanlin
there were two divergent influences on the early development of statisical methods.statistics had a mother who dedicated to keeping orderly records of governmental units(state and statistics come from the same latin root staus)
and a gentlemanly gambling father who relied on mathematics to increase his
skill at playing the odds in games of chance .the influence of the mother on the offspring ,the statistics, is
represented by counting,measuring ,describing ,tabulating ,ordering ,
and the taking of censuses --all of which led to modern descriptive statistics.
from the influence of the father came modern inferential statistics ,which is
based squarly on theories of probability.
descriptive statistics involves tabulating ,depicting ,and describing collections of datas .these data may be quantitative such as measures of height ,intelligence,or grade level--variables that are characterized by an underlying continuum--or the data may represent qualitaive variables ,such as sex ,college major or personality type.large masses of data must generally undergo a process of summarization or reduction before they are comprehensive .descriptive statistics is a tool for describing or summarizing or reducing to comprehensible form the properties of an otherwise unwidely mass of data.
inferential staistics is a formalized body of methods for solving another class of problems that present great difficulties for the unaided human mind .this general class of problems characteristically involve attempts to make predictions using a sample of observations.for example ,a school superintendent wishes to determine the proportion of children in a large school system who come to school without breakfast ,have been vaccinated for flu,or whatever.having a little knowlege of staistics ,the superintendent would know that it is unnecessary and inefficient to question each child :the proportion for the entire district could be estimated fairly accurately from a sample of as few as 100 children .thus ,the purpose of inferential statistics is to predict or estimate characteristics of a population from a knowledge of the characteristics of only a sample of he population,