Statistical Studies
Statistics is concerned with the collection and analysis of data.
There are several different types of statistical studies that are used to collect data.
Let’s take a look at surveys, experimental studies and observational studies.
1. Survey – Statistical surveys are used to collect quantitative information from a specific population. A survey may focus on opinions or factual information depending upon the purpose of the study. Surveys may involve answering a questionnaire or being interviewed by a researcher. The census is a type of survey.
Advantages of surveys:
• can be administered in a variety of forms (telephone, mail, on-line, mall interview, etc.)
• are efficient for collecting data from a large population
• can be designed to focus only on the needed response questions
• are applicable to a wide range of topics
Disadvantages of surveys:
• are dependent upon the respondent’s honesty and motivation when answering
• can be flawed by non-response
• can possess questions or answer choices that may be interpreted differently by different respondents (such as the choice “agree slightly”)
Randomization and a well-designed survey:
A sample population is considered random if the probability of selecting the sample is the same as the probability of selecting every other sample. When a sample is not random, a bias is introduced which may influence the study in favor of one outcome over other outcomes.
2. Experimental study – In an experimental study, the researcher takes measurements, or surveys, the sample population. The researcher then manipulates the sample population in some manner. After the manipulation, the researcher re-measures, or re-surveys, using the same procedures to determine if the manipulation possibly changed the measurements.
During a “controlled” experiment, the researcher will separate the sample population into groups with one group established as the control group. All groups will be manipulated in some manner, except for the control group which will remain the same.
An example of an experimental study:
A group of students is interested in knowing if the number of times they can sink a basketball is related to the color of the basketball. The students shoot a series of baskets and record their success using a regulation colored basketball. They then switch to a blue colored basketball and shoot the same series of baskets. A statistical analysis is performed.
3. Observational study – In an observational study, the sample population being studied is measured, or surveyed, as it is. The researcher does not influence the population in any way or attempt to intervene in the study. There is no experimental manipulation. Instead, data is simply gathered and correlations are investigated.
An example of an observational study:
A group of students is interested in knowing if there is a correlation between attending an SAT Prep class and scores achieved on the SAT Examination. The students use a survey to collect their data from both students who took an SAT Prep class and those that did not take an SAT Prep class. A statistical analysis is performed.