The word statistics is used both in plural as well as in singular sense. In plural sense, statistics means numeric facts which can be used to draw conclusions and in singular sense, it means the statistical methods with the help of which statistical information is used to treat and draw conclusions from them.
There are following limitations of statistics :
Sometimes, when data are not properly collected 1 then there is likelihood to draw wrong conclusions.
Therefore, it is necessary to know the limitations of statistics.
(i) Statistics does not study about individuals : Statistics are expressed in facts. It does not study individuals. For example, there are five students in a class. Statistics only tells the average marks obtained in class not how many marks are obtained by every student in the class.
(ii) It does not study the qualitative aspect of problem : The most important condition of statistical study is that subject of investigation and inquiry should be capable of being qualitatively measured. For example, honesty, poverty, etc.
(iii) Statistics can be misused: The result obtained can be manipulated accordingly to one’s own interest and such manipulated results can mislead the community.
(iv) Statistical results lack mathematical accuracy: The results drawn from statistical analysis are normally in approximates. As the satistical analysis is based on observation of mass data, number of inaccuracies may be present and it is difficult to rectify them.
(v) Uniformity and homogeneity of data : It is essential that data must have the quality of uniformity and homogeneity. Heterogeneous data are not comparable. For example, it would be meaningless to compare the heights of men with heights of trees because these figures are of heterogeneous character.

As there is the problem of choice, the economy has to decide which goods and services are to be produced. For example, which of the consumer goods such as wheat, rice, cloth are to be produced and which of the capital goods such asmachines and tools are to be produced.

When an economy has taken a decision as to what goods or services to be produced, then it has to be about its quantity. How much of consumer goods and capital goods are to be produced. For example, if an economy decides to produce rice and wheat within a given period with limited resources then it will have to using less of machineries.

Meaning: The production possibility curve is the curve which represents all those combinations of two commodities that can be produced with full utilization of resources in the most efficient way, which give the same level of satisfaction to a consumer. 
Properties of PPC:

1. PPC slopes downwards from left to right: It is because in a situation of fuller use of the given resources, production of both goods cannot be increased simultaneously. for example, More of Good X can be produced only with less production of Good Y.
2. PPC is concave to the point of origin: It is because to produce each additional unit of Good X, more units of Good Y will have to be sacrificed. Opportunity cost of producing every additional unit of Good X tends to increase in terms of the loss of production of Good Y. Production will act upon the law of increasing marginal opportunity cost.
3. All points which lie on the PPC are the set of combination of two goods with the full utilization of resources and efficient utilization of technology.

Microeconomics is the study of individuals, households and firms' behavior in decision making and allocation of resources. It generally applies to markets of goods and services and deals with individual and economic issues.

(i) Statistics does not study about individuals : Statistics are expressed in facts. It does not study individuals. For example, there are five students in a class. Statistics only tells the average marks obtained in class not how many marks are obtained by every student in the class.
(ii) It does not study the qualitative aspect of problem : The most important condition of statistical study is that subject of investigation and inquiry should be capable of being qualitatively measured. For example, honesty, poverty, etc.
(iii) Statistics can be misused: The result obtained can be manipulated accordingly to one’s own interest and such manipulated results can mislead the community.
(iv) Statistical results lack mathematical accuracy: The results drawn from statistical analysis are normally in approximates. As the satistical analysis is based on observation of mass data, number of inaccuracies may be present and it is difficult to rectify them.
(v) Uniformity and homogeneity of data : It is essential that data must have the quality of uniformity and homogeneity. Heterogeneous data are not comparable. For example, it would be meaningless to compare the heights of men with heights of trees because these figures are of heterogeneous character.

Long run: Long run is the period in which all the factors of production can be changed to change the output. In a long run, the output can be increased by increasing both variable factors and fixed factors of production. Firms can change fixed factors of production in the long run. 
Output in the long run can be changed by changing the variable and fixed factors of production.

Main sources of the secondary data can be classified into two groups :
1. Published sources :
(a) Government Publications
(b) Semi-government Publications
(c) International Publications
(d) Private Publications
(e) Research Publications
2. Unpublished sources : Secondary Data can be obtained from unpublished sources, because all statistical material is not always published. Studies made by research institutions, scholars etc. can be important sources of secondary data.

An index number is a statistical device for measuring changes in the magnitude of a group of related variables.

Features of Index Number

1. Index numbers are expressed in terms of percentages. However, percentage sign (%) is never used.
2. Index numbers are relative measurement of group of data.
3. Index numbers offer a precise measurement of the quantitative change in the concerned variables over time.
4. Index number show changes in terms of averages.
5. They are expressed in numbers.