Question

What is Sampling? What are the types, advantges  and disadvantages of sampling?

Answer 1

Sampling:

• Sampling is a method of collection of data.
• It is the process of getting a representative fraction of a population.

Sample:

• Sample is the representative fraction of a population.
• In sampling method, a small group is taken from a large
  population. This small group is the sample.
• Analysis of the sample gives an idea of the population.
• When the population is very large or infinite, sampling is the suitable method of data collection.
• For example, One rice is tested from a pot of boiling rice to arrive at
  a conclusion.
• In an electric bulb factory, the bulbs are tested at intervals how long they will burn. If all are tested there is nothing left for selling.
• One grape is tasted before buying a bunch of grapes.
• The oxygen content of pond water can be found out by titrating just 100 ml of water.
• The length of leaves of a neem tree can be calculated by measuring just 10 leaves.
• The food habits of all students of a college can be
  understood by observing only about 100 students.
• There are two types of sampling, namely

1. Random sampling.

2. Non-random sampling.
1. Random Sampling:

• Random sampling is a method of collection of data.
• In random sampling, a small group is selected from a large population without any aim or predetermination.
• The small group selected is called a sample.
• In this method, each item of the population has an equal and independent chance of being included in the sample.
• The random sample is selected by lottery method.
• Each individual is given a number.
• The numbers are written on pieces of papers.
• The papers are put in a box. About 100 papers are picked out. These 100 individuals form a random sample. The analysis of 100 individuals gives an idea of the entire population.
• Random sampling is of 3 types, namely
• 1. Simple random sampling
• 2. Stratified random sampling
• 3. Cluster random sampling
• In simple random sampling, each individual of the population has an equal chance of being included in the sample. In this method, the sample is selected by lottery method.
• In stratified random sampling, the population is divided into groups or strata on the basis of certain characteristics.
• Then the samples are selected by simple random
  sampling.
• For example, we want to select a sample of 100 students from a college population of 1000 students, consisting of 700 girls and 300 boys.
• The whole college population should be divided into two strata.
• One with 700 girls and other with 300 boys.
• Now by simple random sampling method select 70 girls from total of 700 girls and 30 boys from the total of 300 boys.
• In cluster sampling, the whole population is divided into a number of relatively small clusters or groups.
• Then some of the clusters are randomly selected.
• For example, if we want to survey the general health of the college student in a state consisting of 5000 colleges.
• Here we consider cach college as a cluster.

Now we can randomly select several college and conduct the survey.

2. Non-Random Sampling:

• Non-random sampling is a method of collection of data.
• In this method, a sample is collected from a large population based on the convenience, judgement anc consideration of the investigator.
• In non-random sampling, each individual does not ge a chance of being included in the sample.

Eg. If 20 students are selected from a college of 1000 students, the investigator selects 20 representatives.

Advantages of Sampling:

1. Sampling is an economical method of data collection.
2. It saves time, expenditure and energy.
3. It is reliable.

Disadvantages:

1. Sampling needs skill.

2. It needs experts.
3. All the individuals are not represented.

Sampling:

• Sampling is a method of collection of data.
• This is the process of getting a representative fraction of a population.