### Statistics Phase 1 : Population Data vs Sample Data

POPULATION DATA vs SAMPLE DATA

We are starting with Descriptive Statistics . Discriptive Statistics is a branch of statistics that deals in determining the characteristics and features  of the data provided.

The first question that needs to be answered is whether the data provided is the Population data or the Sample data.

Now what is Population data? Population is the collection of all items of interest of our study. For eg the collection of data of all residents of a country is the population data in the National Census Survey study.  Now the size of this data will be very large and it will be very costly and time consuming to obtain this data and to analyse it. So to overcome these problems we make use of Sample data.

Sample data is a subset or a part of the Population data. We generally make use of the Sample data in our analysis because it’s size is less than the Population data and it’s collection and analysis is time and cost effective. For eg.  In our study of studying defects in motorcycles produced by a certain company we can collect a sample of motorcycles and check defects on those sample motorcycles
Now to determine that the sample is a good sample or not we have to check that whether the sample is random and representative of the population.
A random sample is a sample in which sample data is collected randomly from the population data and there is no bias
The probability of selection of each element of population is same. A representative sample is a sample that accurately reflects the population and have same features and characteristics to that of the population. If our population includes different groups then sample data should have elements from all the groups to fully reflect the population.
For eg in selecting the motorcycles we must select the sample in a random way such that chance of selection of each cycle is same. Also our sample must include cycles of both type(gear and non-gear) so that it is a true representative of the population

The objective of collecting population data is to identify the characteristics and features of the population while the objective of sample data is to make judgements and inferences about the population which cannot be analysed due to time and cost constraints.