Variables and Measurement
A researcher measures stress by counting how many times a participant checks their phone during a 30-minute task. What type of measure is this?
Observational measure
The researcher is directly observing and counting behavior
The participant is not rating themselves
There is no questionnaire or scale involved
A researcher wants to know whether caffeine affects memory. Participants are randomly assigned to drink either a cup of caffeinated coffee or a cup of decaffeinated coffee. After 20 minutes, all participants complete the same memory test. What is the independent variable in this study?
Type of coffee (caffeinated vs decaf).
This makes sense because:
The researcher assigns the coffee type
Coffee type is what differs across conditions
Research manipulated this
A researcher wants to test whether background music affects concentration. One group studies in a room with classical music, and another group studies in silence. However, the classical music group happens to have mostly younger students, while the silence group has mostly older students. What is a potential confounding variable in this study?
Age of participants
Why?
A confounding variable varies systematically with the IV (music vs silence)
Age could also affect concentration, so differences might be due to age, not music
A researcher wants to test whether sleep affects memory. Each participant is tested on memory after one night of normal sleep and again after one night of sleep deprivation. What type of research design is this?
Within-subjects design
Why?
The same participants experience both conditions
Each person serves as their own control, reducing variability
A researcher finds that students who spend more time studying tend to get higher exam scores. What kind of relationship does this illustrate?
Positive correlation
Why?
As one variable (study time) increases, the other (exam score) also increases
Correlation does not imply causation
Participants rate their happiness on a scale from 1 (“not happy at all”) to 7 (“extremely happy”).
What scale of measurement is this?
Ordinal
The numbers represent an order (more happy vs less happy)
But we can't assume equal spacing between the numbers
The difference between 1 and 2 may not equal the difference between 6 and 7
In the same study, the researcher records how many words each participant correctly recalls on the memory test. What is the dependent variable in this study?
Memory test performance (number of words recalled)
Why this makes sense:
DV is the outcome being measured
It depends on the IV (coffee type)
Participants are told they are in a memory study and asked to memorize a list of words. Some participants realize the purpose of the study is to test recall ability and try extra hard to memorize the words. What type of bias might this introduce?
Demand characteristics
Why?
Participants change behavior because they guess the purpose of the study
This can alter results independent of the experimental manipulation
In a study of a new study technique, one group of students uses flashcards, while another group studies by rewriting notes. Different students are in each group. What type of research design is this?
Between-subjects design
Why?
Different participants are in each condition
No participant experiences more than one level of the IV
A study finds that people who eat more ice cream also report more sunburns. Why can we not conclude that ice cream causes sunburns?
There could be a third variable (like hot weather).
Why?
Another variable (temperature/sun exposure) affects both ice cream consumption and sunburns
This is a third-variable problem
Researchers are conducting a study where reaction time is recorded in milliseconds. What scale of measurement is this?
Ratio Scale
Reaction time has all four properties:
Ordered values (longer vs shorter time)
Equal intervals (each millisecond is the same length)
A true zero (0 ms means no reaction time)
Ratios are meaningful (200 ms is twice as long as 100 ms)
A researcher studies the effect of study environment on learning. One group studies the material in complete silence, while another group studies the same material while listening to music. After studying, all participants take the same exam. Identify the independent and dependent variables in this study.
IV = study environment (silence vs. music)
DV = exam score
Why this makes sense:
IV = what changes between groups (study environment)
DV = measured result (exam score)
A researcher unintentionally praises participants in the experimental group more than those in the control group during a learning task. What type of bias is this?
Experimenter bias
Why?
Experimenter behavior systematically favors one group
Can influence the DV and threaten internal validity
Participants complete Task A and then Task B. Their performance on Task B is worse than Task A, possibly because they are tired from completing Task A. What type of threat does this scenario illustrate?
Order effect
Why?
The sequence of tasks affects performance
Carryover from Task A (like fatigue) changes Task B results
Participants are randomly assigned to drink either 2 cups of coffee or 0 cups. Their alertness is measured after 30 minutes. The coffee group shows higher alertness scores. Why can the researcher infer a causal relationship here?
Because it is a true experiment with random assignment
Why:
Random assignment controls for confounds
The IV (coffee) is manipulated, DV (alertness) is measured
True experiments allow causal inference
A study is conducted where they record eye color (blue, brown, green, hazel). What scale of measurement is this?
Nominal Scale
Categories are names only
There is no order
No category is greater or less than another
A psychologist wants to examine whether lighting affects creativity. Participants are assigned to work in either a brightly lit room or a dimly lit room. After completing a creative writing task, their creativity is scored by independent raters. What is the independent variable in this study?
Lighting condition (bright vs. dim)
Why this makes sense:
The researcher manipulates lighting
Creativity scores are measured after the manipulation
A study on problem-solving uses only psychology majors as participants, but the researcher wants the results to generalize to all adults. Which type of validity is threatened?
External validity
Why?
External validity is about generalizability
A sample of only psychology majors may not represent the general population
Participants in an experiment perform almost perfectly on a learning test regardless of the teaching method they received. What problem does this scenario illustrate?
Ceiling effect
Why?
DV scores are clustered near the maximum
Differences between conditions are masked because everyone scores near the top
A researcher asks 100 people how many hours they sleep each night and how happy they feel on a daily basis. They find that people who sleep more tend to report higher happiness. Which of the following is true about this relationship?
More sleep is moderately associated with higher happiness, BUT causation can't be determined
Why?
This shows a positive association between sleep and happiness
We cannot say that more sleep causes people to be happier
Other factors (like health or stress) could explain the relationship
A researcher measures stress by collecting saliva samples and recording cortisol concentration. What type of measurement is this?
Objective measure
Data is collected using biological recording
The participant’s opinion or interpretation doesn't matter
The measurement exists independently of self-report
A researcher examines the relationship between diet and weight loss. Participants choose whether they want to follow a low-carb diet or a low-fat diet for three months. At the end of the study, weight loss is recorded. Why is diet not a true independent variable in this study?
Because participants self-selected their diet. No random assignment was used.
Remember:
A true IV must be randomly assigned / manipulated
Self-selection introduces bias and confounding, preventing causal conclusions
A happiness questionnaire asks participants to rate how “morally good” they are alongside happiness questions. Scores suggest participants are very happy, but the researcher realizes participants may be answering to look good rather than truthfully. Which type of validity is most clearly being threatened?
Construct validity
Why?
Construct validity is about whether a test really measures what it’s supposed to measure
If participants answer based on social desirability, the measure doesn’t accurately reflect true happiness
A researcher studies the effects of two independent variables on memory: study method (reading vs. drawing) and lighting (bright vs. dim). Each participant is randomly assigned to one of the four possible combinations. What type of research design is this?
2×2 factorial design
Why?
There are two IVs, each with two levels
All combinations are tested in different participants
A researcher records how many hours teenagers spend on social media each day and the number of hours they spend exercising each week. The results show that teenagers who spend more time on social media tend to exercise less. How should this relationship be interpreted?
Teenagers who spend more time on social media tend to exercise less, but we cannot conclude that social media use causes less exercise.
Why?
This shows a negative association: as social media time increases, exercise decreases
Causation can't be inferred because other factors (like busy schedules, work, or sports participation) could influence both variables