Sampling Methodology (includes line transect and belt transect methods) Stratified sampling is used to take into account distinct sections (or strata) that are recognized within **the main body** of a habitat when samples are obtained at specified intervals, generally along a line. For example, if vegetation was being sampled across a forest floor, then stratification would be based on **soil type** (sand, loam, etc.) or some other natural division of the habitat. Samples could also be taken at random within each stratum. However, this would result in a relatively small number of samples representing each stratum, reducing the statistical power of the study.

Systematic sampling is used when it is desirable to obtain samples from every unit in a population, so that no matter how many individuals are in the population, all will receive an equal chance of being selected for inclusion in the sample. Systematic sampling can also be used when it is desirable to ensure that certain characteristics of interest are represented in the sample. For example, if the goal is to select plants that are either tall or short, then these should be considered criteria for selecting plant units instead of using random selection. The simplest form of systematic sampling is random starting point and fixed interval sampling. In this method, subjects are chosen randomly with respect to their position in the population, but they are examined at regular intervals.

Systematic sampling is a form of probability sampling approach in which sample members are drawn from a larger population at random but with a set, periodic interval. The sampling interval is determined by dividing the population size by the desired sample size. > span>

There are two types of systematic samples: simple and complete.

In **a simple system**, each sample member is selected independently at random from the overall population. That is, there is no special relationship between the selection of any one sample member and that of any other. For example, if we were to use a simple system when selecting 100 people for a survey, we could select **every person** at random using a random number table. There would be no design or pattern to the sample, because it would be impossible to predict how many people would be selected or **what groups** they might come from.

A complete system includes every member of the population. This means that the first sample member is selected by randomly choosing an address from the mailing list or directory, for example. Then, every nth member after that will be selected, where "n" is the sample size. For example, if we were to use a complete system when selecting 100 people for a survey, we would start with someone who lives at 123 Pleasant Street and then select **every 25th person** after that until all 100 had been selected.

There are three methods: Sampling at random Sampling stratification Sampling methodicalness.

Random sampling is the simplest and most common method for **sample surveys**. In this method, a representative sample of the population being studied is selected by randomly choosing certain numbers from a list or table of contents. Random samples are useful for estimating values for populations that cannot be obtained otherwise. For example, if there was no way to select individuals at random from a large group, then using a random sample would be the only way to estimate the percentage of people in the group who have a particular trait-for example, those who have blue eyes or black hair. Random samples can also be used to select cases (e.g., patients) or controls (e.g., healthy people) for study purposes.

Stratified sampling is used when you want to examine differences between groups but don't want to risk having underrepresentative samples from any one group. For example, if there were significant differences between young adults and older adults in terms of how many times they watch television per day, it wouldn't be feasible to use **a single sample** since it would include too many young adults who probably watch **very few television programs** and too many older adults who probably watch much more than that.