1.3 Data Collection and Sampling Techniques

To obtain samples that are unbiased, that give each subject in the population an equally likely chance of being selected - statisticians use four basic methods of Sampling

Random, Systematic, Stratified, and Cluster sampling.

Stratified sampling

Dividing the population into subgroups or strata according to some characteristic relevant to the study. Then subjects are selected at random from each subgroup.

Random sampling

All members of the population have an equal chance of being selected.

State which sampling method was used. Out of 10 hospitals in a municipality, a researcher selects one and collects records for a 24-hour period on the types of emergencies that were treated there.

Cluster because the researcher divided the population into groups (clusters) and randomly selected one of them to collect data from.

Identify the sampling method that was used. For 15 minutes, all customers entering a selected Walmart store on a specific day are asked how many miles from the store they live.

Convenience Sampling: All customers entering a selected Walmart store on a specific day are surveyed, which is convenient but may not be representative of all Walmart customers.

Identify the sampling method that was used. In a medical research study, a researcher selects a hospital and interviews all the patients that day.

Convenience Sampling: The researcher selects a hospital and interviews all the patients that day, which is convenient but may not be representative of the larger population.

Cluster sampling

Dividing the population into sections or clusters and then selecting one or more clusters at random and using all members in the cluster(s) as the members of the sample.

There is sampling method statistician use called: the convenience sample.

Imagine you're a researcher and you need to collect data for a study. But you don't have much time or resources. So, what do you do? You might decide to just gather data from people who are easily available to you. Maybe they're your friends, family, or colleagues. Or maybe they're people passing by on the street. This is what we call a convenience sample.

State which sampling method was used. The subscribers to a magazine are numbered. Then a sample of these people is selected using random numbers.

Random

Identify the sampling method that was used. In a large school district, a researcher numbers all the full-time teachers and then randomly selects 30 teachers to be interviewed.

Random Sampling: All the teachers are numbered and then a random selection of 30 teachers is made.

Identify the sampling method that was used. Ten counties in Pennsylvania are randomly selected to determine the average county real estate tax that the residents pay.

Random Sampling: Ten counties in Pennsylvania are randomly selected, which ensures each county has an equal chance of being selected.

Systematic sample

Selecting every Kth member of the population where K is a counting number

Identify the sampling method that was used. To determine how long people exercise, a researcher interviews 5 people selected from a yoga class, 5 people selected from a weight-lifting class, 5 people selected from an aerobics class, and 5 people from swimming classes.

Stratified Sampling: The population is divided into subgroups (strata) based on the type of exercise class, and then a sample is taken from each subgroup.

State which sampling method was used. A researcher divides a group of students according to gender, major field, and low, average, and high grade point average. Then she randomly selects six students from each group to answer questions in a survey

Stratified because the researcher divided the population into subgroups based on some relevant characteristic, and then randomly selected a sample from each subgroup.

One of the most common method used for Data Collection is:

Surveys: 1. Telephone surveys 2. Mailed questionnaire surveys 3. Personal interview surveys

State which sampling method was used. Every 10th bottle of Energized Soda is selected, and the amount of liquid in the bottle is measured. The purpose is to see if the machines that fill the bottles are working properly.

Systematic

Identify the sampling method that was used. To check the accuracy of a machine filling coffee cups, every fifth cup is selected, and the number of ounces of coffee is measured.

Systematic Sampling: Every fifth cup is selected, which is a systematic approach.