What is exactly the difference among Indicator, Index, Variable and Measure? I would appreciate some reference.
Without context, all that can be said is to collect some common usages:
An indicator wide sense is anything that indicates (i.e. is considered revealing or diagnostic), which could be any counted or measured variable. Consider statements such as that unemployment rate, GDP growth and government debt are good indicators of the state of an economy. In contrast, an indicator precise sense indicates the state of a binary or dichotomous variable (e.g. survived vs not, alive vs dead, present vs absent, male vs female) by 1 or 0. Often, which state is coded 1 and which is 0 is a matter of convention or convenience, as in the case of male or female. Indicator variables are perhaps more often called dummy variables in several fields of statistical science, although that term on occasion has been misread as offensive.
An index is sometimes a scaled composite variable: for example, a price index or wages index is based on a weighted sum of prices or wages, often scaled so it is 100 in some base year or at some base time. An index is also sometimes any kind of summary measure designed to capture some property (segregation, diversity, whatever) in a single number. Ideally, it is recognised whenever one index is used that others are also possible.
A variable varies, or at least in principle might vary. It is difficult to say more if that is unclear, except by contrast: anything defined to be constant cannot be a variable. Statistics makes enormous play, however, with parameters which are constant in a given situation but variable from situation to situation. So, mean temperature and the slope of a regression line are parameters.
A measure may or should be something with a strict definition in measure theory (http://en.wikipedia.org/wiki/Measure_theory), but either you know that already or it is irrelevant to you. At elementary or introductory or lay level, it might just be yet another word for anything you (count or) measure (e.g. one measure of diversity in ecology is just the number of species present at a site).
I don't think any of these terms is really difficult -- at the level I have chosen here -- and any good dictionary should provide authority if you need it. That said, there are numerous formal accounts or theories of measurement, which do not all agree on terminology or definitions.
Indicators are qualitative and quantitative variables, used for measuring change.
Index: compound or composite indicators are called Indexes. Which means one index might be a collection of different indicators, such as "Quality of Public Services" which is an index, and it can be measured through different indicators, that might include "Public Satisfaction level of Government service delivery" and some other indicators.
Variables take different values. That is categorized either in qualitative and quantitative variables or dependent and independent variables.
Indicator is variable that can measure change against objective. For example, we set an objective like life style of people improved. Indicator for this objective will be: % of household having refrigerator at their home. Via this indicator we can measure the progression (improve life style or condition of people).
Variable means changeable and characteristic of something,. It may be number like 3, 5, 8 or a word like age, income, and expanse. Considering above definition in somehow it is also indicator.
Measure means calculating some numbers or gauging some things.
Index has close definition to indicator, some time we use it interchangeably. On the other hand index also means list of words.