Sampling Design


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Sampling Design

  1. 1. Sampling Design <ul><li>Census & Sample Survey </li></ul><ul><li>All the items in any field of inquiry constitute a “Universe” or “Population” </li></ul><ul><li>A complete enumeration of all items in the population is known as Census Inquiry </li></ul><ul><li>Most times census inquiry is not practically possible </li></ul>
  2. 2. Sampling Design… <ul><li>Sample Survey – selection of a few items of the population </li></ul><ul><li>The respondents selected should be representative of the total population </li></ul><ul><li>The sampling process is called the sampling technique </li></ul><ul><li>The survey so conducted is known as the sample survey </li></ul><ul><li>The researcher must prepare a sample design for his study – that is, how a sample should be selected and what size such a sample would be </li></ul>
  3. 3. Steps in Sample Design <ul><li>The following are crucial: </li></ul><ul><li>Type of Universe – define the set of objects, technically called the Universe, to be studied </li></ul><ul><li>Sampling Unit – sampling unit may be a geographical one (district, city, village) or it may be a social unit (family, club, school) or it may an individual </li></ul><ul><li>Source List – also known as ‘sampling frame’ from which the sample is to be drawn. It contains all items of a universe </li></ul>
  4. 4. Steps in Sample Design… <ul><li>Size of Sample – refers to the number of items to be selected from the universe to constitute a sample; a major issue here is – the size should neither be excessively large nor too small. An optimum sample is one which fulfills the requirements of efficiency, representative ness, reliability and flexibility </li></ul><ul><li>Budgetary Constraint – cost considerations have a major impact upon decisions relating to the size of the sample </li></ul>
  5. 5. Steps in Sample Design <ul><li>Sampling Procedure – finally, the type of sample to be used, that is, the technique to be used in selecting the items for the sample. There are several sample designs, from which the researcher can choose. </li></ul>
  6. 6. Criteria of Selecting a sampling Procedure <ul><li>There are two costs involved in a sampling analysis – the cost of collecting the data and the cost of an incorrect inference resulting from the data </li></ul><ul><li>The researcher, therefore, must be aware of the two causes of incorrect inferences: a) systematic bias b) sampling error </li></ul>
  7. 7. Criteria of Selecting a sampling Procedure… <ul><li>A systematic bias results from errors in the sampling procedures and it cannot be reduced or eliminated by increasing the sample size </li></ul><ul><li>Sampling Errors are the random variations in the sample estimates around the true population. Generally, sampling errors decreases with the increase in the size of the sample </li></ul>
  8. 8. Types of Sample Designs <ul><li>All the sample designs are based on two factors – the representation basis and the element selection technique </li></ul><ul><li>Representation Basis – the sample may be probability sampling or non-probability sampling. Probability sampling is based on the concept of random selection; non-probability sampling is “non – random” sampling </li></ul>
  9. 9. Types of Sample Designs… <ul><li>Element Selection Basis – the sample may be either restricted or unrestricted. Unrestricted sampling is when each element is drawn individually from the population at large. Restricted sampling is when all other forms of sampling are used. </li></ul><ul><li>Thus, sample designs are basically of two types: 1. Probability Sampling </li></ul><ul><li>2. Non-Probability Sampling </li></ul>
  10. 10. Non-Probability Sampling <ul><li>Is that sampling procedure which does not afford any basis for estimating the probability that each item in the population has of being in included in the sample </li></ul><ul><li>Also known as deliberate sampling, purposive sampling and judgment sampling </li></ul><ul><li>Here, items for the sample are selected deliberately by the researcher, that is, purposively choose the particular units of the universe for constituting a sample on the basis that the small mass that they select out of a huge one will be representative of the whole. Ex.s – if the economic condition of people living in a state are to be studied, a few towns and villages may be purposively selected for intensive study on the principle that they can be representative of the entire state. </li></ul>
  11. 11. Non-Probability Sampling… <ul><li>Here, personal element (bias) has a great chance of entering into the selection of the sample </li></ul><ul><li>However, if the investigators are impartial, work without bias and have the necessary experience – the results obtained may be tolerably reliable. </li></ul>