Psyc 301

carry over effect

an effect that carries over form one experimental condition to another It is the possibility that effects from previous treatments may still be present when delivering new treatment, thus affecting the outcome of the new treatment.

treatment

another word for a condition of an experiment

Latin square

control procedure in which each subject experiences each condition in a different order from other subjects

block randomization

control procedure in which the order of conditions is randomized but with each condition being presented once before any condition is repeated

matching

control procedure to ensure that experimental and control groups are equated on one or more variables before the experiment

counterbalancing

controlling for order and sequence effects by arranging that subjects experience the various conditions in different orders

mixed factorial designs

designs containing at least one variable that is presented in a within subjects fashion and one other variable that is presented in a between subjects fashion

replication

repeating an experiment to see if the results will be the same

quasi experiment

research procedure which does not meet the requirements of a true experiment

random sampling

selecting a group of subjects for study from a larger population, each individual is chosen entirely by chance and each member of the population has an equal chance of being included in the sample

control group

subjects in a between subjects design experiment who are like the experimental group in every respect except that they do not receive the treatment

experimental group

subjects in an experiment who receive treatment

random assignment

unbiased assignment process that gives each subject an equal and independent chance of being placed in every condition

interaction

when the effect of one independent variable depends on the level of another independent variable

Example of repeated testing

Due to time constraints, the experiment was run over four consecutive days. On Day 1, children viewed the 20-minute cartoon (Control condition). On Day 2, the Generalization Probe was conducted. On Day 3, the children were exposed to the 20-minute interactive video (Experimental condition). Finally, on Day 4, a second Generalization Probe was conducted. The mean score for children on the first Generalization Probe was 1.2 and their mean score on the second Generalization Probe was 3.4. We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

Example of maturation

During a class early in the school year, the children viewed the 20-minute cartoon (Control condition). Two days later, the Generalization Probe was conducted. The experimenter fell ill soon afterwards, and so it wasn't until a class late in the school year that the children viewed the 20-minute interactive video (Experimental condition). Two days after that, a second Generalization Probe was conducted. The mean score for the children on the first Generalization Probe was 1.2 and their mean score on the second Generalization Probe was 3.4. We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

Experimenter bias (threat to validity)

Expectations of an outcome by persons running an experiment may significantly influence that outcome. As with instrumentation, the reliability of the instrument used to gauge the dependent variable or deliver the independent variable is suspect, but here the reason for that unreliability is the impartiality of persons in direct contact with the subjects or the data. Suppose that subjects in two comparison groups differ with respect to the independent variable. Suppose also that the experimenter is responsible for administering the appropriate condition to each group and measuring the dependent variable. If scores on the dependent measure differ between the two groups, the discrepancy may be due to the independent variable or to differential treatment of the two groups by the experimenter who is under the influence of his or her hypothesis.

Experimental mortality (threat to validity)

In the course of an experiment, some subjects may drop out before it is completed. Suppose that subjects in two comparison groups differ with respect to the independent variable. Suppose also that subjects in one group are more likely to discontinue their participation part way through an experiment than subjects in another group and that dependent variable is measured at the end of the experiment. If scores on the dependent measure differ between those subjects remaining in the two groups, the discrepancy may be due to the independent variable or to a unique characteristic of subjects able to endure a particular condition, a subject-related variable that would be disproportionately present in each group.

advantages of a within subjects design

Increases efficiency in data collection; fewer participants, no need for extra control group like between subjects need, Increases validity; participants may approach tasks in diff ways, here same context is used, increased statistical sensitivity, reduces extraneous variables, increase in statistical power; each participant act as there own control, increase chance of finding significant difference if real difference.

advantages of a between subjects design

Individual score is independent of other scores Can be used for a wide variety of research questions/hypothesis - any experiment comparing two/more treatment conditions Help to avoid practice effects and other 'carry-over' problems that result from taking the same test twice.

Example of selection

It so happened that there were an equal number of boys and girls in the classes, so for convenience the boys were assigned to the Control Group and the girls to the Experimental Group. One day at school, the boys were told to go to one room and the girls to another room, where they were exposed to their respective conditions. Two days later, the Generalization Probe was conducted. The mean score for children in the Control Group was 1.2 and the mean score for children in the Experimental Group was 3.4. We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

Example of selection-maturation

It so happened that there were an equal number of boys and girls, so for convenience the boys were assigned to the Control Group and the girls to the Experimental Group. During a class early in the school year, a Generalization Probe was conducted for all children. The experimenter fell ill soon afterwards, and so it wasn't until a class late in the school year that the children in the comparison groups were separated, with the Control Group children viewing the 20-minute cartoon and the Experimental Group children viewing the 20-minute interactive video. Two days after that, a second Generalization Probe was conducted. To see the results, click here (1). We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

Example of regression to the mean

One day at school, the children viewed the 20-minute cartoon (Control condition). Two days later, the Generalization Probe was conducted. Then, in a class the following week, the children viewed the 20-minute interactive video (Experimental condition). The plan was to administer a second Generalization Probe two days after that. However, at this point, the experimenter realized that she had insufficient funding to complete the study and would only be able to retest ten children. She selected the ten poorest performing children on the first Generalization Probe, the mean score of which was 0.1. Their mean score on the second Generalization Probe was 2.5. We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

History (threat to validity)

Outside events may influence subjects in the course of the experiment or between repeated measures of the dependent variable. Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. Suppose also that Event A occurs between Time A and Time B. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to Event A.

Selection-maturation (threat to validity)

Subject-related variables and time-related variables may interact. Suppose that subjects in two comparison groups differ with respect to the independent variable and a subject-related variable such as age. Suppose also that the dependent variable is measured twice for each group, once at Time A and later at Time B, and that the independent variable is introduced in the interim. If the change in scores on the dependent measure from Time A to Time B differs between the two groups, this discrepancy may be due to the independent variable or to distinctive naturally occurring developmental processes for the two age categories that comprise the two comparison groups.

selection (threat to validity)

Subjects bring with them into the investigation unique characteristics, some learned and some inherent. Examples include sex, height, weight, color, attitude, personality, motor ability, and mental ability. If assigning subjects to comparison groups results in unequal distribution of these subject-related variables, then there is a possible threat to internal validity. Suppose that subjects in two comparison groups are unlike with respect to the independent variable and one of these subject-related variables. If scores on the dependent measure differ between the groups, the discrepancy may be due to the independent variable or to the subject-related variable.

Maturation (threat to validity)

Subjects may change in the course of the experiment or between repeated measures of the dependent variable due to the passage of time per se. Some of these changes are permanent (e.g., biological growth), while others are temporary (e.g., fatigue). Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to naturally occurring developmental processes.

Regression to the mean (threat to validity)

Subjects with extreme scores on a first measure of the dependent variable tend to have scores closer to the mean on a second measure. According to Campbell (1969, p. 414): "Take any dependent measure that is repeatedly sampled, move along it as in a time dimension, and pick a point that is the "highest (lowest) so far. On the average, the next point will be lower (higher), nearer the general trend." Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. Suppose also that value observed for subjects at Time A is considerably higher (lower) than would typically be the case. If scores on the dependent measure differ at these two times, it may be due to the independent variable or to a regression artifact.

Word superiority lab

The existence of a WSE generally implies that there is some type of access or encoding advantage that words have in the mind that pseudowords or single letters do not have. Various studies have proposed that the distinction is a result of pronounceability differences (nonwords are not pronounceable and therefore are not as easily remembered), frequency (real words are more frequently encountered and used), meaningfulness (real words have semantic value and therefore are better retained in memory), orthographic regularity (real words follow familiar spelling conventions and are therefore better retained in memory), or neighborhood density (real words tend to share more letters with other words than nonwords and therefore have more activation in the mind). Other studies have proposed that the WSE is heavily affected or even induced by experimental factors, such as the type of masking used after the presentation of the word, or the duration of the masks. A trial will start with a fixation point. Focus on it. One second later, two stimuli will be shown, either two words or two nonwords. The words or nonwords will either be the same or will differ by just one letter. Your task is to decide if they are the same or different.

Example of experimenter bias

The name of each child in the classes was written on a separate slip of paper. All the slips were put in a bowl and mixed up thoroughly. Students were assigned to the Experimental Group and to the Control Group alternately as their names were pulled out of the bowl one at a time. One day at school, children in the Control Group were told to go to one room and children in the Experimental Group to another room, where they were exposed to their respective conditions. Two days later, the Generalization Probe was conducted. For ease of record keeping, all the Control Group children were tested first, then all the Experimental Group children. Both the student teacher, who recorded how the children responded to the confederate's lures, and the confederate who presented the lures, were heavily involved in the production of the interactive video, and both of them strongly believed in its efficacy. The mean score for children in the Control Group was 1.2 and the mean score for children in the Experimental Group was 3.4. We can conclude that the 20-minute interactive video was effective in changing what the children did in a potential abduction situation.

Example of experimental mortality

The name of each child in the classes was written on a separate slip of paper. All the slips were put in a bowl and mixed up thoroughly. Students were assigned to the Experimental Group and to the Control Group alternately as their names were pulled out of the bowl one at a time. One day at school, the children in the Control Group were told to go to one room and children in the Experimental Group to another room, where they were exposed to their respective conditions. Some of the children in the Experimental Group appeared bored by the interactive video, became disruptive, and were removed from the room. Two days later, the Generalization Probe was conducted. The mean score for children in the Control Group was 1.2 and the mean score for the remaining children in the Experimental Group was 3.4. We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

Example of instrumentation

The name of each child in the classes was written on a separate slip of paper. All the slips were put in a bowl and mixed up thoroughly. Students were assigned to the Experimental Group and to the Control Group alternately as their names were pulled out of the bowl one at a time. One day at school, the children in the Control Group were told to go to one room and children in the Experimental Group to another room, where they were exposed to their respective conditions. Two days later, the Generalization Probe was conducted. For ease of record keeping, all Control Group children were tested first, then all the Experimental Group children. The student teacher scored children's responses to the confederate's lures. In the beginning, he hid indoors and strained to see and hear through an open window; later on, he discovered he could see and hear better by hiding outside and peeking around a corner. The mean score for children in the Control Group was 1.2 and the mean score for children in the Experimental Group was 3.4. We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

Example of history

The name of each child in the classes was written on a separate slip of paper. All the slips were put in a bowl and mixed up thoroughly. Students were assigned to the Experimental Group and to the Control Group alternately as their names were pulled out of the bowl one at a time. One day at school, the children in the Control Group were told to go to one room and the children in the Experimental Group to another room, where they were exposed to their respective conditions. Immediately afterwards, while walking back to their regular classroom, all the children in the Control Group saw a man laughing and joking with their school principal. Two days later, the Generalization Probe was conducted, during which many of the Control Group children recognized the stranger as the man who made their principal laugh. The mean score for children in the Control Group was 1.2 and the mean score for children in the Experimental Group was 3.4. We conclude that the 20-minute interactive video improved the children's self-protection skills in a potential abduction situation.

Repeated testing (threat to validity)

The prior measurement of the dependent variable may affect the results obtained from subsequent measurements. Suppose that the dependent variable is recorded twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to the procedure involved in measuring the dependent variable at Time A.

Instrumentation (threat to validity)

The reliability of the instrument used to gauge the dependent variable or manipulate the independent variable may change in the course of an experiment. Examples include changes in the calibration of a mechanical measuring device as well as the proficiency of a human observer or interviewer. Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. Suppose also that the ability of a recording device to detect instances of the target behavior improves (declines) as the experiment progresses. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to more (less) sensitive recordings of the target behavior at Time B relative to at Time A.

control condition

a condition in a within subjects design experiment that does not contain the experimental manipulation

nuisance variable

a condition in an experiment that cannot easily be removed and so is made an independent variable as a means of control

nonequivalent control group

a group of subjects that is not randomly selected from the same population as the experimental group

condition

a group or treatment in an experiment

control

any means used to rule out threats to the validity of research

sequence effect

changes in a subject's performance resulting from interactions among the conditions themselves

order effect

changes in a subject's performance resulting from the position in which a condition appears in an experiment

main effect

in a factorial experiment, the effect of one independent variable, averaged over all levels of another independent variable

level

in an experiment, a particular value of an independent variable

ceiling-effect interaction

interaction in which one variable has a smaller effect when paired with higher levels of a second variable

antagonistic interaction

interaction in which the two independent variables tend to reverse each other's effect

synergistic interaction

interactions in which the two independent variables reinforce each other's effects

Internal validity

it shows a cause and effect relationship between the independent and dependent variables

statistical control

mathematical means of comparing subjects on paper when they cannot be equated as they exist in fact

reverse counterbalancing

method of control in which conditions are presented in order the first time and then in reverse order

individual differences

personality, intelligence, ability, IQ, interests, values, self concept, self efficacy, and self esteem

within subjects experiment

research design in which each subject experiences every condition of the experiment

between subjects experiment

research design in which each subject experiences only one of the conditions in the experiment

factorial design

research design that involves all combinations of at least two values of two or more independent variables

multiple conditions design

research design that involves more than two conditions

true experiment

research procedure in which the scientist has complete control over all aspects

factors

the independent variables of an experiment

two conditions design

the simplest research design, involving only two conditions