What is the difference between "Universe" and "Population"?

Universe and Population are the two very common terms, Definitely, you know the two terms. Even though the two terms are considered as same and used interchangeably, However, both should be clearly understood in the context of statistics and research. Such as how the universe is defined? And How the population is defined in statistics and research? How do the two terms differ from each other and how do they similar to each other, that means for which case the population is said to be the universe? Here you will get the answers to all the questions. 

Universe

From the statistical point of view, the term 'universe' refers to the total of the items or units in any field of enquiry. 

For example; 

• Total number of screws produced by a manufacturing unit in a week constitutes the universe
• Total number of calls received by a call center in a week can be considered a universe
  
  
  

Population

Now turn to population. The term 'population' refers to the total of the items about which the information is desired or the set of all items or measurements in which the investigator is interested.

For example;

• Average length of the number of screws produced in an hour
• Average call duration of the number of calls received in an hour.

The Focus of the Population

The population focuses on a particular characteristic such as; average length of the screws or the average call duration of the calls. And the number of units possessing this characteristic constitutes the population like; a hundred thousand screws or a ten thousand calls

Now to get the average length of the number of screws produced in an hour, we take random samples of screws at different points of time in that particular hour. Same way to get the average call duration of the number of calls received in an hour, we take random samples of calls at different points of time in that hour.

When the Population and Universe are said to be the same?

But in which case, the population is considered the universe? That's the big question!  

Universe or population can refer to the same thing and can be considered synonym if the population you use while choosing your samples includes all the items of the universe.

For example: 

If you take samples from the screws produced in a week which we considered a universe, here in this case the population and universe are the same thing. Similarly, if you take samples from the calls received in a week that was also considered a universe, here again, the population and universe are the same thing.

Finite and Infinite Population

Finite Population

Now let's try to understand the finite and infinite population. 

The population or universe can be finite and infinite. The population is finite if we can enumerate or count all the items in the population.

For example:

• The number of people living in a city
• The number of workers in a factory
• Number of calls received in an hour

Capital 'N' is generally used to indicate the number of items in the population.

Infinite Population

In the case of infinite population, theoretically, it is impossible to observe all the items. 

Thus in an infinite population, the number of items is infinite. We can't have any idea about the total number of items, which means we can't enumerate or count the all the items in an infinite population such as:

• The number of stars in the sky 
• Rivets manufactured in a company
• Births of the insects

But the point to remember is that an infinite population of physical objects does not exist in the true sense. In spite of the fact that many such populations appear to be very very large. 

Hence for practical consideration, the infinite population is infinite because we can't count all the elements of the population in a reasonable period of time. And therefore we use the theoretical concept of infinite population as an approximation of a very large finite population.