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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. |
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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.
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Advantages of surveys: |
Disadvantages 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
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• 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") |
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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.
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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.
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An example of an experimental study:
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| 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.
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An example of an
observational study:
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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.
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