In a malaria survey every 1st and 4th house was choosen for survey. The type of samplining -
Ans. is 'b' i.e., Systemic random sampling * Types of random sampling are: -i) Simple random sampling# It is also known as "unrestricted random sampling". Each individual is chosen randomly and entirely by chance. There is no stratification in similar groups. Thus, each individual has the same probability of being chosen.# Methods of simple random sampling are : -i) Lottery methodii) Random number tableiii) Computer technique.# It is suitable for small homogenous population and is used in clinical trials. It provides the greatest number of possible samples.ii) Systemic random sampling# In order to do systematic random sampling, the individuals in a population are arranged in a certain way (for example, alphabetically).# A random starting point is selected and then every nth (for example 10th or 15th) individual is selected for the sample.# That is, after arranging the individuals in certain pattern (e.g., alpabetically) a starting point is chosen at random, and choices thereafter at regular intervals.iii) Stratified random sampling# When sub-populations vary considerably, it is advantageous to sample each subpopulation (stratum) independently.# Stratification is the process of grouping members of the population into relative hemogenous subgroups before sampling.# The strata should be mutually exclusive, every element in the population must be assigned to only one stratum. Then systematic random sampling method is applied within each stratum.# Stratified random sampling is particularly useful where one is interested in analysing the data by a certain characteristic of the population, viz Hindus, Muslims, Christians, age group etc, - as we know these groups are not equally distributed in the population.iv) Cluster sampling# Cluster sampling is a sampling technique used when natural groupings are evident in a statistical population. In this technique, the total population is divided into these groups (or clusters) and a sample of groups is selected.# The characteristic feature is that selected groups act as samples (while in other types of random sampling individuals act as sample).# Cluster sampling is rapid, simple and economic (less expensive).# Sample size may vary according to study.# Cluster sampling is an example two-stage sampling.# There are chances of sampling error.# Cluster sampling is used in India to evaluate immunization coverage. WHO used 30 x 7 technique (total = 210 children) for cluster sampling in which there are 30 clusters, each containing 7 children who are 12-23 months old and are completely immunized for primary immunization (till measles vaccine at 9 month).v) Multistage random sampling# It is done in successive stages; each successive sampling unit is nested in the previous sampling unit. Advantage: Introduces flexibility in sampling.# For example, in large country surveys, states are chosen, then districts, then villages, then every 10th person in village as final sampling unit.vi) Multiphse random sampling# It is done in successive phase; part of information is obtained from whole sample and part from the sub-sample.# For example, in a TB survey, Mantourx test done in first phase, then X-ray done in all Mantoux positive, then sputum examined in all those with positive X-ray findings.
Cluster samling
Systemic random sampling
Stratified random sampling
Multistage sampling
Epidemiology