Chapter 10 - Manipulating Variables
placebo effect
this response occurs if participants have expectations about the effects of an experimental condition (e.g., the effects of a medication).
Which of the following illustrate contamination by communication?
A participant shares details about a research study with a future participant.
Why is it difficult to control for a history threat?
History threats may involve unanticipated factors outside of a researcher's control.
Identify the appropriate method to prevent an instrumentation threat.
Properly calibrate all measurement instruments.
During a drug trial, the experimental group receives a drug designed to decrease symptoms of anxiety and the control group receives a placebo. Which of the following would exemplify a history threat?
The experimental group receives training in mindfulness during their checkups.
Why are confounds a concern in an experimental study?
They make it unclear what was responsible for a change observed in the dependent variable
In an experimental design, why is it important that the groups have equivalent experiences?
To be sure that any differences in participants' behavior relative to the dependent variable are due solely to differences in the independent variable.
instrumentation
a change in the measuring device during the course of a study.
Contamination by communication
a confound that occurs when participants who have been seen by the researcher communicate their experiences with those who are waiting their turn to participate, such that the waiting participants' foreknowledge of the experiment confounds the study.
random assignment
a method of assigning participants such that each participant has an equal chance of being placed into each condition or group in an experiment, as opposed to other nonrandom means of assignment (e.g., having participants self-select their condition or group).
Block design
a research design in which participants are divided into relatively homogeneous subsets, or blocks, based on a variable of interest, and from these blocks they are randomly assigned to the experimental or control conditions. The purpose of a block design is to ensure that a characteristic of the study participants that is related to the target outcome is distributed equally across conditions.
matched-pairs design
a research design involving two groups of participants in which each member of one group is paired with a similar person in the other group (i.e., someone who matches them on one or more variables that are not the main focus of the study but nonetheless could influence its outcome).
After controlling for participant variables in an experimental study,
a researcher must still control for equal experiences between groups during the experiment.
homogenous sample
a sample group that is unified or similar on all relevant variables.
double-blind study
a study design in which both the participants and the researchers are unaware of each participant's study condition. This design has low potential for experimental bias.
single-blind study
a study design in which the participants are unaware of their study condition. The intent of this design is to avoid experimental bias.
longitudinal study
a study that takes place over a period of time, sometimes several years.
placebo
a therapeutically inert substance or nonspecific treatment.
confounding variable
a variable other than the independent variable that causes a change in the dependent variable. It is conceptually distinct but empirically inseparable from one or more independent variables; it is a type of "extra" variable that the researcher has not accounted for in an experiment.
Using a within-group design, researchers were studying the influence of food with differing sugar content on participant energy levels. They planned to provide a food high in sugar content and measure participant energy levels 30 minutes later and provide a food low in sugar content and measure participant energy levels 30 minutes later. What should be included in the research design to increase internal validity?
a washout period
counterbalancing
an arrangement of the experimental conditions in which multiple orders of the experimental conditions are administered and compared; different sequences are assigned to different participants or groups.
A researcher is concerned with confounding variables in
an experimental research design
A researcher was concerned that the research assistants she used to code the experimental videos in her study may have been coding for slightly different behaviors. If the experimental group behaviors were coded in a different way than the control group behaviors, this is an example of
an instrumentation threat
A researcher who is trying to prevent contamination by communication could
ask participants not to discuss the study details with others during or after their participation in research.
A researcher finds that the average income of participants in her experimental group is higher than that of participants in her control group, so she switches some participants from the experimental to the control group before any data is collected. This is an example of
balancing groups as a whole
A researcher is investigating the effectiveness of various new medications to reduce alcohol cravings among a diverse group of participants. To eliminate confounding participant variables, the researcher splits the participant pool into 4 subsets of participants who are similar in age and weekly alcohol consumption. She then randomly assigns participants in each subset to take one of the 3 medications or the placebo. What strategy is she using to control for confounding participant variables?
block design
participant variables
can influence the dependent variab;e
Participant variables
characteristics that make people unique: age, sex, ethnicity, education, socioeconomic status, marital status, living arrangements, employment status, personal habits, personality traits, and so on. Participant variables cannot be manipulated in experiments.
An instructor decided to test different study methods with the morning and afternoon sections of her research methods course. The morning section received instructions to study by rereading their notes, and the afternoon section received instructions to study by coming up with new examples of each term. Each section received the same test during their normal class period. Identify the confound.
class time
equivalent
comparable
During pretest, a researcher presents participants with a group of digital three-dimensional mazes and measures completion time. The researcher then has participants engage in 30 minutes of aerobic activity. During posttest, participants complete the mazes again, and the researcher measures completion time. A testing effect would indicate that
completion time during the second test is changing due to repeated testing.
interrater reliablity
consistent judgment among observers or evaluators such that results do not vary significantly from one to another.
A researcher had half of the participants begin with exposure to Condition A—a large computer monitor—and half of the participants begin with Condition B, a smaller computer monitor. Completion times for a data search and entry task were recorded following each condition. The design of this study includes _____, which can detect an order effect.
counterbalancing
A researcher was interested in whether a new method of teaching fractions was more effective for student learning. She had an assistant randomly assign participants, who had no understanding of fractions, to either a new technique group or to an old technique group prior to testing. All participants then completed the same math test as a measure of their learning. In this scenario, neither the researcher nor the participants knew if they were assigned to the new technique group or the old technique group. This would be considered a _____ study.
double blind
Identify the strength of within-group research designs.
eliminate participant variables
A researcher is concerned that participants may perform better at posttest simply because they completed the measure a second time and not from an improvement due to experiencing the independent variable. To prevent this practice effect, the researcher could
eliminate the pretest.
Confounds are a threat to which of Mill's criteria for establishing causality?
elimination of alternative explanations
To investigate the effect of presentation format, a researcher randomly assigned participants to a video group or an audio group. The same information was presented for both groups; however, the format differed. The groups had an equal number of participants, but the video group had twice the number of male participants as the audio group. Recall of the presented material was measured for both groups. The confound in this example is
gender
A researcher is investigating the effectiveness of a smoking cessation program among middle-aged, college-educated White men who have been smoking cigarettes since they were teenagers. What strategy is the researcher using to eliminate confounding participant variables?
homogeneous sample
During an experimental study, all aspects should be equal for the groups except for the
independent variable
A researcher notes that a participant performs more poorly during the experimental condition compared with the control condition, but this difference is confounded with a change over time—fatigue. During the experimental condition, the participants had already been participating in the study for more than 1 hour. This threat to internal validity is known as
maturation
Which of the following threats to internal validity is the most difficult to prevent?
maturation
maturation
naturally occurring time-related changes in participants.
To avoid an internal validity threat from regression to the mean, researchers should
not select participants based on extreme pretest scores.
Which of the following internal validity threats does not apply to both within-group and between-groups designs?
order effect
A researcher conducted a within-group study to investigate the difference in spatial problem-solving between 5-year-old children when they were distracted and when they were not distracted. The group was presented with an online maze while having a cartoon playing next to them, and time to complete the maze was measured. After a 10-minute break, the same group of children was presented with a similar online maze while a colored screen appeared next to them, and time to complete the maze was measured. An example of an order effect would be if
participants perform faster in the control condition only because it was the second exposure to an online maze.
A researcher was investigating how well a new antianxiety medication decreased anxiety for patients with moderate levels of anxiety. The participants in the experimental group were given the new medication, and participants in the control group were not. The researcher found a decrease in anxiety for the experimental group. If the participants might have had a decrease in anxiety because of their expectations about the effect of the medication and not the medication by itself, this would indicate which of the following possible threats to internal validity?
placebo effect
A researcher is investigating the effectiveness of a new yoga program and assigns participants to either the experimental condition or control condition such that each person has an equal likelihood of being assigned to either condition. This strategy is called
random assignment
A researcher is interested in investigating whether the presence of a night-light in a room has an effect on sleep quality. She asks participants in both the experimental and control groups to take a short nap in a darkened room in the laboratory, but for participants in the experimental group, she leaves a night-light on before exiting the room. The participants do not know of the night-light manipulation. This is an example of a __________ study.
single blind
internal validity
the degree of confidence with which we can conclude that only variations in the independent variable—and not the action of other confounding variables—caused observed changes in the dependent variable.
order effect
the influence of the order in which treatments are administered.
random selection
the process of randomly choosing participants (i.e., choosing your sample), whereas random assignment is the process of randomly deciding the experimental condition to which each participant will be exposed.
Fifty participants were randomly assigned to a physical activity group or a relaxation group during a research study examining self-control. The two research assistants conducting the study decided to split the workload so that one of them would test the experimental group participants and the other would test the control group participants. This study design is problematic because
the research assistant conducting the test was different for each condition.
history effect
the tendency of events or circumstances outside an experiment to influence the outcome, particularly in pretest-posttest studies.
regression to the mean
the tendency of extremely high or extremely low scores to become more moderate (i.e., closer to the mean) with repeated measurement of the dependent variable.
testing effect (practice effect)
the tendency of participants who are tested multiple times to be influenced by this "practice" in a way that changes their performance in subsequent tests.
washout period
the time frame allotted for an administered drug to be eliminated from the body or for a previously administered intervention to become ineffective.
A researcher plans to study the effect of cardio exercise versus weight lifting on motivation. She randomly assigns half the participants to attend a weight-lifting class at the gym next door to the lab twice a week in 45-minute blocks and the other half to attend a cardio class at the same gym three times a week in 30-minute blocks. She then measures motivation each week over a 2-month period. A possible confound in this study is
time spent in the gym
Why might a researcher try to gather participants from various locations?
to prevent contamination by communication