POPULATION,SAMPLE AND SAMPLING Group of individual under study is called population. It may be finite orinfinite. A part selected from the population is called sample The process of selecting a sample is called sampling. If there are C(N,n) types of sample then size of the sample is n that can be picked up from a population of size N
PARAMETERS AND STATISTICSThe constants of population are Mean (µ) Standard deviation (σ) both of them are called PARAMETERSMean and standard deviation of a sample are known as STATISTICS.
TYPES OF SAMPLING PURPOSIVE SAMPLING RANDOM SAMPLING STRATIFIED SAMPLING SYSTEMATIC SAMPLING PURPOSIVE SAMPLINGPurposive sampling targets a particular group of people. When the desiredpopulation for the study is rare or very difficult to locate and recruit for astudy, purposive sampling may be the only option. Example: if u want to study on the population who are suffering from blood cancer. It is quiet difficult population to find.
RANDOM SAMPLING Each element in the population have equal probability of selection andeach combination of an element have equal probability of selection Random numbers to select from an ordered list Example: names drawn from a hat
STRATIFIED SAMPLINGDivide population into groups that differ in important waysBasis for grouping must be known before samplingSelect random sample from within each group. Example: let us consider we all students are population and divide these into two groups one who wearing specs and other who don’t.It reduces error than the random sampling.
SYSTEMATIC SAMPLING It is a statistical method involving the selection of elements from anordered sampling frame. The most common form of is an equal-probability method, in which everykth element in the frame is selected, where k, the sampling interval k=N/n Where n is the sample size and the N is the population size.Example: Suppose a supermarket wants to study buying habits of their customers, then using systematic sampling they can choose every10th or 15th customer entering the supermarket and conduct the study on this sample.
STANDARD ERROR Standard error is the standard deviation of sampling distribution. It is used for accessing the difference between the expected value andobserved value.