Most commonly used statistical sampling methods are shown below.
- Random sampling
- Stratified sampling
- Cluster sampling
- Systematic sampling
Random sampling
Each member in the population has equal chance to being selected. This can be used when the population is homogeneous.
- E.g. – Select the plant leaves randomly for the measure the photosynthetic rate
- E.g – Plant specimens are randomly collected for the make a herbarium.
Stratified sampling
Population is divided into subgroups or strata then random samples are collected from the subgroups. this useful when the population is heterogeneous.
- E.g. – In a agricultural land is divided base on the particular disease is present or absent and then random samples are selected from the each subgroups and then analysis the diseases resistance,
- E.g. – Particular plant is group into base on their geological location, random samples are collected from the each group and analysis the geological variation and genetic variability.
Cluster sampling
Population is divided into clusters, then the samples are randomly selected from these clusters. all individual in cluster is included in the sample(1 cluster = 1 sample) this can used form homogeneous or heterogeneous population, mostly used in geologically separated population.
- E.g. – For particular plant species select the cluster from different geological regions and analysis their genetic variance.
Systematic sampling
Sample is selected from the system, this is used for ordered or patterned population.
- E.g. – Draw a line alone the forest and count the number of tree having DBH more than 1.5 m
