Ch 8Collection of Data — Class 11 Economics, concept-first.

Every study in economics rests on evidence, and that evidence usually takes the form of numbers. The purpose of collecting data is precisely to provide such evidence, so that a problem can be understo…

Statistical data can be obtained from two kinds of source, and which one applies depends on who first gathered the figures.

To collect primary data, a researcher runs a survey — a method of gathering information from individuals by asking them questions.

The most common survey instrument is the questionnaire (also called an interview schedule). It may be self-administered — filled in by the respondent alone — or administered by the researcher, an enum…

Once the instrument is ready, the data must actually be gathered. There are three basic modes of data collection:

In a personal interview the researcher (or investigator) conducts a face-to-face conversation with each respondent. It is used when the researcher can reach all the members to be studied.

In a mailing questionnaire survey the questionnaire is sent to each individual by post (or, today, online or by SMS), with a request to complete it and return it by a fixed date.

In a telephone interview the investigator asks the questions over the phone.

Before running the full survey it is advisable to try the questionnaire on a small group first. This trial is called a Pilot Survey or pre-testing of the questionnaire.

After deciding how to collect data, the researcher must decide how much of the group to study — everyone, or only a part. This gives two approaches:

A survey that includes every element of the population is a Census or the Method of Complete Enumeration.

In statistics the Population (or Universe) means the totality of the items under study — the whole group to which the results of the study are meant to apply.

Random sampling selects the individual units from the population at random, so that every unit has an equal chance of being included.

In non-random sampling the units are not chosen by chance, so not every unit has an equal chance of being selected; instead the convenience or judgement of the investigator decides who is included.

Whenever we estimate a population's characteristics from a sample, errors can creep in. A population of numerical values has two features of interest here: its Central Tendency, measured by the mean,…

The purpose of a sample is to produce one or more estimates of the population parameters (a parameter being the actual value of a characteristic of the whole population, such as its average income).

Non-sampling errors are more serious than sampling errors: a sampling error shrinks as the sample grows, but a non-sampling error is hard to reduce even with a large sample, and it can occur even in a…

Sampling bias is a type of non-sampling error that arises from a flaw in the sampling plan itself. It occurs when the plan is designed in such a way that some members of the target population could no…

A non-response error is a non-sampling error that occurs when the investigator is unable to obtain information from a unit that was actually selected in the sample.

An error in data acquisition arises from recording incorrect responses. If a teacher asks students to measure the length of a table, their measurements will differ because of differences in the measur…

Several agencies at the national and state level collect, process and tabulate statistical data. National-level bodies include the Census of India, the National Sample Survey (NSS), the Central Statis…

Economic facts expressed in numbers are called data, and the purpose of collecting them is to understand, explain and analyse a problem and the causes behind it.

Key points of the chapter: