While all of these are things that a good experiment should possess, the one that is most important for a study’s ability to generate conclusions about causal relationships is the presence of a true independent variable. The fact that the researcher manipulates this variable directly allows him or her to conclude that any changes in the dependent variable are related to the changes in the manipulated independent variable alone. Causal relationships could still be inferred from a study that does not have a consent form or proper confidentiality practices; however, this study would certainly be unethical. Even research studies that do not focus on causal relationships involve the measurement of dependent variables.

Random assignment is the only term that is incorrectly matched. Random assignment involves assignment to experimental and control groups. It ensures that each participant has an equal chance of being assigned to a group. On the other hand, random selection refers to each member of a group having an equal chance of being selected for the study. 

Cross-sectional and longitudinal studies are both types of correlational studies that allow researchers to predict or draw conclusions from data. "Cross-sectional" studies allow researchers to examine how a sample differs on a specific characteristic at one point in time. "Longitudinal studies" involve following a sample over time. On the other hand, "experimental studies" include random selection, random assignment, and an independent variable that is manipulated. Causation can only be concluded from true experiments. In "double-blind experiments," both the researchers and participants are unaware of which groups are assigned as the experimental and control groups. Last, a "meta-analysis" allows researchers to look at several research studies and draw statistical conclusions. 

The independent variable is the specific group that participants are assigned to (i.e. drug vs. sugar pill group). The experimental group is the group that receives the intervention (i.e. new depression drug), while the control group is the group that receives no treatment or a placebo. The dependent variable in a study is what is being measured, which in the case of this study is depression scores. The term random assignment refers to each participant having an equal chance of being assigned to the experimental and control groups. 

The key difference between projective and objective personality tests is the way they are scored. Objective tests, which often involve self-report methods and “true/false” or multiple choice questions, are scored in a standardized, predetermined way. For example, if Joe and Anne both bubble in the exact same set of answers for a certain personality test, their score reports will show the exact same results. Contrastingly, projective tests generally don’t use a hard-coded method of scoring participant responses. Instead, the psychologist interprets a freeform response to an ambiguous stimulus and attempts to infer meaning from it, sometimes using guides created for this task as a reference. Both the Thematic Apperception Test (TAT) and the Rorschach Inkblot Test are projective tests. The TAT uses ambiguous, uncaptioned scenes as the ambiguous stimuli, while the Rorschach uses monotone, symmetrical inkblot splatters as the ambiguous stimuli.

Naturalistic observation refers to watching individuals in their “natural habitat” when laboratory observation would be cost-prohibitive, impossible, or otherwise unrealistic. The defining feature of naturalistic observation is watching individuals and recording data about their behaviors in the normal, unaltered environment. This can be useful when the individuals might change their behavior when they are aware they’re being watched (i.e. a phenomenon sometimes called the Hawthorne effect). The example involving sitting at a park is naturalistic observation, because the researcher is observing the behavior of parents of children at play in their natural environment, as opposed to bringing the parent-children pairs into a lab and then observing the parents’ behavior. The other examples all involve bringing human subjects into a lab setting, which by definition is not naturalistic observation.

The correct answer is "electroencephalography (EEG)." In EEG, the researcher applies electrodes to the participant’s (or patient’s) scalp and records the electrical signals emitted by the brain. Recall that neurons communicate with one another using electrical impulses. The electrodes are placed in specific places that allow the researcher to measure activity in different areas of the brain. This technique is often used in sleep research.

Double blind studies collect experimental data to draw conclusions, not correlational data! In other words, researchers are able to examine cause and effect relationships due to the random assignment of participants to a control group or an experimental group.

A Pearson correlation between two variables indicates that as one variable increases, another variable either increases or decreases by some amount in a linear manner.

Correlations range between  and , with  signifying the strongest possible negative correlation between two variables,  signifying the strongest possible positive correlation, and  signifying the complete absence of any correlation between two variables.