Primary Data : Primary Data is that data which is collected by the investigator or researcher himself. It is an original form of data collection.
1.Primary data is always original as it is col-lected by the investigator.
2.Suitability of the primary data is positive because it is systematically collected.
3.Primary data is expensive and time consum-ing.
4.Extra precautions are not required.
5.Primary data is in the shape of raw material.
6.Possibility of personal prejudice exists.
7.Investigating agency collects the data.
8.Requires long time for collection.
9.More reliable and suitable to the enquiry because the investigator himself collects it.
10.Requires elaborate organisation.
Secondary Data : Secondary Data refers to that data which is collected through other sources.
1.Secondary data lacks originality. The investi-gator makes use of the data collected by other agencies.
2.Secondary data may or may not suit the objects of enquiry.
3.Secondary data are relatively cheaper.
4. It is used with great care and caution.
5.Secondary data is usually in the shape of readymade products.
6.Possibility of lesser degree of personal prejudice.
7.Some other investigating agency collects it for its own use.
8.Requires less time for collection.
9.Less reliable and suitable as someone else has done that job of collection which may not serve the purpose.
10.Needs comparatively less funds.

In business, the Production Possibility Curve (PPC) is applied to evaluate the performance of a manufacturing system when two commodities are manufactured together. The management utilizes this diagram to plan the perfect proportion of goods to produce to reduce the wastage and cost while maximizing profits.

The two main characteristics of PPC are:

1. Slopes downwards to the right: PPC slopes downwards from left to right. It is because in a situation of fuller utilisation of the given resources, production of both the goods cannot be increased simultaneously. More of commodity A can be produced only with less production of commodity B.
2. Concave to the point of origin: It is because to produce each additional unit of commodity A, more and more units of commodity B will have to be sacrificed. Opportunity cost of producing every additional unit of commodity A tends to increase in terms of the loss of production of commodity B. Production will act upon the law of increasing marginal opportunity cost.

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.

Median may be defined a the middle value in the data set when its elements are arranged in a sequential order, that is, either in ascending or descending order of magnitude. It concentrates on the middle or centre of a distribution.

According to Connor, "The median is that value of the variable which divides the group into two equal parts, one part comprising all parts greater, and the other values less than median."

According to Horace Secrist, "Median of a series is the value of the item actual or estimated when a series is arranged in order of magnitude which divides the distribution into two parts."

According to Croxton and Cowden, "the median is generally defined as the value which divides the distribution so that an equal number of items is on either side of it."

Merits:

1. The median is useful in case of frequency distribution with open-end classes.
2. The median is recommended if distribution has unequal classes.
3. Extreme values do not affect the median as strongly as they affect the mean.
4. It is the most appropriate average in dealing with qualitative data.
5. The value of median can be determined graphically where as the value of mean can not be determined graphically.
6. It is easy to calculate and understand.

Demerits:

1. For calculating median it is necessary to arrange the data, where as other averages do not need arrangement.
2. Since it is a positional average its value is not determined by all the observations in the series.
3. Median is not capable for further algebraic calculations. 
4. The sampling stability of the median is less as compared to mean.

The main difference between customer and consumer is that the customer is the person who buys or purchases the products or the services while the consumer is the person who uses the products or the services.

A measure of central tendency is a single value that describes the way in which a group of data cluster around a central value. To put in other words, it is a way to describe the center of a data set. There are three measures of central tendency: the mean, the median, and the mode.