Sampling (statistics and probability)
- 2. The process of obtaining information from a subset(sample) of a larger group(population). The results for the sample are then used to make estimates of the larger group. Faster and cheaper than asking the entire population. SAMPLING
- 3. Get information about populations Reduce cost of research More accuracy of results Less field time Generalize about population When it’s impossible to study the whole population WHY SAMPLING?
- 4. Technical Terms • A sampling frame is a list of sampling units. • A sample is a collection of sampling units drawn from a sampling frame. • Parameters: numerical characteristics of a population • Statistic: numerical characteristic of a sample
- 5. Probability Sample: A method of sampling that uses of random selection so that all units/case in the population have an equal probability of being chosen. Non-Probability Sample: Does not involve random selection and methods are not based on the rational of probability theory Sampling Techniques Probability Non-Probability TYPES OF SAMPLING
- 6. Probability SAMPLING Following are some commonly used sampling methods: • Simple Random Sampling • Stratified Random Sampling • Cluster Sampling • Systematic Sampling
- 7. SIMPLE RANDOM SAMPLING Application when population is small, homogeneous & readily available All subsets of the frame are given an equal probability. Each element of the frame thus has an equal probability of selection. A table of random number or lottery system is used to determine which units are to be selected.
- 8. Possible Ways To Do Sampling • The sampling units are chosen with replacement in the sense that the chosen units are placed back in the population. • The sampling units are chosen without replacement in the sense that units are chosen are not placed back in the population.
- 9. Properties of Sample Distribution
- 10. Advantages: • Easy method to use • No need of prior information of population • Equal and independent chances of selection to every element Disadvantages: • If sampling frame large, this method impracticable. • Does not use researcher’s expertise . • Larger risk of random error