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Week 8

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Selection and Assignment Methods
Before you look at the data-based examples, consider some specific ways researchers find
participants and why people choose to participate in research studies. This is important to
consider because it is the fishing place, the method, and the bait, or the incentive, that make the
difference relative to whom is attracted to a study.
Ways to Find Participants
Participants must come from somewhere, and they must be drawn into participating by some
means. The sample for a research study is usually selected from the community or from college
students. People in the community often participate because they are interested in the study for
some reason, or they want the money being offered, and college students usually participate for
class credit.
When researchers attempt to find participants, they may place advertisements or circulate
information about the purpose of the study and the types of people needed. They send
information through various media, and these media tend to attract specific demographic groups.
For example, if researchers place an advertisement in a newspaper near the crossword puzzles,
they will find people who tend to look at that section. If the investigators are conducting a study
on cognitive changes with age, then, they are likely to find participants who are functioning
relatively well because most of them will find the advertisement by reading the information. The
media source is like a fishing pond. After the investigators choose a pond, they must decide what
bait to use as a lure. The bait is the information contained in the advertisement.
See the linked document for reasons people do, and do not, choose to participate in a study.
Impact of Self-Selection on Research
In this week, you will study a real-life example of how self-selection may alter or bias a study.
How Self-Selection Impacts a Research Study
Look at some data from the caffeine and attention study and alter the participant sample to see
how the data changes. This exercise will help you see how the study results and external validity
may be impacted.
Biased and Nonbiased Samples
Consider another example to understand the relationship between biased and nonbiased samples.
View the linked file for an example of descriptive statistics for a biased sample.
Next, consider the biased study near the homeless shelter again to see how a biased sample may
alter the results of a study.
Check Your Understanding
Consider that you have placed an advertisement for a biased study near a homeless shelter to
study the relationship between the amount of caffeine ingested and the level of alertness. When

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you monitored food intake data among the participants, you found the people who were recruited
near the shelter had a significantly higher food intake. Studies have shown that there is an
inverse relationship between the amount of food in a person’s stomach and liquid absorption.
This means, as the food intake increases, the absorption of the caffeinated drinks would decrease.
What if you failed to find a relationship between the amount of caffeine ingested and the level of
alertness?
Select the conclusion that you would draw from the study.
You failed to find a relationship because the absorption of the caffeine was decreased due to
participants stuffing their stomachs.
You failed to find a relationship because the attention scores would decrease in direct proportion
to the reduced caffeine consumption.
If you selected (a), you are correct. It demonstrates how a biased sample can alter the results of a
research study.
Data Collection and Technology
Technology is being used for research assessment at an increasing rate and there are many
advantages and some disadvantages to using it in research. During this series of lectures, you
will primarily concentrate on the use of computer technology in psychological research. You will
explore the use of computers for presenting stimuli and for measuring responses.
Although psychologists used machines to present stimuli long before computers were around,
computers have opened up a whole new world of possibilities. The positive aspect of using
computers in our daily lives and as a tool for research is hard to ignore. Computers improve the
quality of information presented to the participants in psychological studies.
While there are plenty of benefits in using computers to present information to participants in
research studies, there are a few weaknesses, or cons, to consider.
Let’s look at both the positive and the negative contributions that computers have made to
research.
See the linked document for the pros and cons of using of technology to present stimuli.
Now that you have studied both the pros and the cons for presenting stimuli, let's discuss the
strengths and weaknesses of using computer technology for measuring participant responses.
Pros and Cons of Automated Measurement
There are pros and cons to using computers for automated measurement.
Pros for Using Computers for Automated Measurement:
Computers and other special types of technology can be used to collect data on behaviors that
would otherwise be missed by the human sensory system. The advantage to using technology is

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Selection and Assignment Methods Before you look at the data-based examples, consider some specific ways researchers find participants and why people choose to participate in research studies. This is important to consider because it is the fishing place, the method, and the bait, or the incentive, that make the difference relative to whom is attracted to a study. Ways to Find Participants Participants must come from somewhere, and they must be drawn into participating by some means. The sample for a research study is usually selected from the community or from college students. People in the community often participate because they are interested in the study for some reason, or they want the money being offered, and college students usually participate for class credit. When researchers attempt to find participants, they may place advertisements or circulate information about the purpo ...
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