Sampling

probability sampling

A method of sampling that uses some form of random selection. Every member of the population must have the same probability of being selected fro the sample, since the sample should be free of bias and representative of the poplation. Ex: - simple random sampling - systemic sampling - stratified random sampling - cluster sampling

Cluster sampling:

A population is divided into clusters using naturally occurring geographic or other boundaries. Then, clusters are randomly selected and a sample is collected by randomly selecting from each cluster. The sampling technique is less costly and more efficient than simple random sampling, especially when the population is spread across a wide geographic region.

Sample:

A subset of elements drawn from a population to draw conclusions or make estimates about the larger population.

Sampling by state is an example of which sampling method? cluster sampling convenience sampling snowball sampling simple random sampling

Correct Answer: cluster sampling Cluster sampling is a form of probability sampling involving the division of the population into clusters (usually by geographic region), before taking a random sample of each cluster. Convenience and snowball sampling are examples of non-probability sampling.

Which type of sampling occurs when a group of physical therapy students conducting a research study utilize their classmates as the sample population? simple random sampling convenience sampling cluster sampling systematic sampling

Correct Answer: convenience sampling Convenience sampling is a non-probability sampling method that involves the selection of a sample population that is readily available and logistically convenient. The remaining options are probability sampling methods that involve a form of random selection of subjects.

Which term is best described as the complete collection of elements to be studied? cohort group population sample

Correct Answer: population The population is referred to as the complete collection of elements to be studied or stated differently, the group to which the results of research are intended to be generalized.

Systematic sampling and cluster sampling are examples of which type of sampling method used in human research? probability sampling non-probability sampling sampling with replacement snowball sampling

Correct Answer: probability sampling Systematic sampling and cluster sampling are examples of probability sampling since both methods utilize a form of random selection of subjects. Other forms of probability sampling include simple random sampling and stratified random sampling.

Which sampling method would be the most desirable when a research study involves human subjects? probability sampling without replacement non-probability sampling without replacement probability sampling with replacement non-probability sampling with replacement

Correct Answer: probability sampling without replacement Sampling without replacement is a sampling method in which a unit selected from the population is not returned to the population and therefore, cannot be selected again for the same sample. This form of sampling is most often used with research studies involving human subjects. Probability sampling is preferable because it eliminates researcher bias in the selection of subjects.

Researchers investigating the effects of an intervention on an extremely rare genetic condition would most likely utilize which sampling method? simple random sampling systematic sampling cluster sampling purposive sampling

Correct Answer: purposive sampling Purposive sampling involves the selection of subjects based on predefined criteria chosen by the investigators. This sampling method is often utilized when the population being studied is small.

Which of the following sampling methods is an example of non-probability sampling? stratified random sampling simple random sampling cluster sampling quota sampling

Correct Answer: quota sampling Non-probability sampling does not involve random selection of subjects. Quota sampling is an example of non-probability sampling that involves convenience sampling after stratification.

Flipping a coin to determine which participants in a study are in the control group versus the treatment group is a form of: blinding crossover matching randomization

Correct Answer: randomization Randomization is used to achieve a balance between treatment and control group subjects and to avoid investigator bias. Methods of randomization range from using complicated software to simply flipping a coin.

The best way to create representative experimental and control groups is by assigning participants through: randomization availability self-selection precision matching

Correct Answer: randomization Randomization is used to achieve a balance between treatment and control group subjects and to avoid investigator bias. Methods of randomization range from using complicated software to simply flipping a coin.

Which sampling method involves asking current research subjects to identify the names of other potential participants? convenience sampling simple random sampling snowball sampling cluster sampling

Correct Answer: snowball sampling Researchers using snowball sampling ask current subjects to identify other potential subjects. Snowball sampling is used when the characteristic to be studied is rare and it is extremely difficult or costly to identify individuals with this characteristic.

Purposive sampling

Subjects are deliberately selected based on predefined criteria chosen by the investigators.

simple random sampling

Subjects have an equal chance of being selected for the sample. Sampling method often relies on a table of random numbers or a number generator on a computer to determine the sample. However, simple random sampling is not the most statistically efficient method of sampling and my not result in a representative sample, since it is the luck of the draw.

Mean

The arithmetic average; the sum of all the values divided by the number of values

Sampling error:

The chance difference between the statistic calculated from a sample and the true value of the parameter in the population. Sampling error is inherent in the use of sampling methods.

Population:

The complete collection of elements to be studied. The group to which the result of research are intended to be generalized.

Median:

The point on a distribution at which 50% of the values fall above or below. It is the 50th percentile. The median is identified by first rank ordering the values. If the number of values is odd, the median is the middle value. If the number of values is even, the median is the mean of the two middle numbers.

Convenience sampling:

The sample is selected from subjects who are convenient or readily available to the researcher.

Mode:

The value that occurs most frequently. A distribution with two modes is termed bimodal. A distribution of more than two modes is termed multimodal.

Stratified random sampling

also called proportional or quota random sampling, the population is divided into homogenous subgroups (strata) and then a simple random sample is drawn from each. Stratified random sampling assures that the sample will be representative of key subgroups of the population in addition to the overall population.

non-probability sampling

any method of sampling that does not involve random selection of subjects. - convenience sampling - purposive sampling

Systemic Sampling

subjects are selected by taking every nth subject from the population. The size of the interval is based on the size of the population and the desired sample size. The greatest advantage associated with this sampling technique is its simplicity.