Samples & Population Flashcards
What is a Statistic?
The quantity calculated solely from the observations in a sample. It does not involve any unknown parameters
(i.e. a statistic is a numerical property of a sample)
What is a Population?
A collection of individual people/ items
How can a Population be finite?
It is finite if it is possible to know exactly how many members there are in the population
e.g.- the number of students at a particular school – You can give each student a number, and count how many of them there are
How can a population be infinite?
It is infinite if it is impossible to know exactly how many members there are in the population
e.g. - number of grains of sand on a stretch of beach – it would be impossible to count them all
How can a population be countably infinite?
It is countably infinite if we know the population could be infinite, but in practice we can count the number of individual members of it
e.g. - the number of throws of a dice in order to obtain a 6
What is a census?
If information is to be obtained from all members of the population, the investigation is known as a census
What are the Advantages of taking a census?
Every single member of the population is used
It’s unbiased
It gives an accurate answer
What are the Disadvantages of taking a census?
Takes a long time
Costly
Often difficult to ensure the whole population has been tested
What is a Sample?
Some subset of the population which is intended to be representative of the population
What are Sampling Units?
Individual units of a population
What is a Sampling Frame?
When the sampling units of the population are individually named/number to form a list
What are the Advantages of Sampling?
Representative of the whole population (if the population is large + well mixed)
Cheaper
Advantageous when testing results in destruction
Data is more readily available
What are the Disadvantages of Sampling?
Uncertainty due to natural variation of the sample
Uncertainty due to possible bias
What is a Population parameter?
Any characteristic of the population which is measurable
What is a Sampling Distribution?
All possible samples are chosen from a population; the values of a statistic and the associated probabilities is a sampling distribution
