Experimental Psych Exam 2

Statistics give us a way to tell apart ____ ____ from random individual differences.

real effects

descriptive statistics

• used to describe/summarize the data.

• many types: frequency distributions, summary measures, and graphical representations of the data

• way to visualize the data

• first step in any statistical analysis

Cross-Tabulation

• a way to see the relationship between two nominal or ordinal variables

  • when done with score data, it is usually done as a scatter plot

• create a set of cells by listing the values of one variable as columns and the values of the other as rows

histograms

can be used to graph either

• data representing discrete categories

• data representing scores from a continuous variable

frequency polygon

like a histogram except that the frequency is shown with a dot above the score, with the dots connected.

two frequency polygons

• can compare two or more frequency polygons on the same scale

• easier to compare groups because the graph appears less cluttered than multiple histograms.

If the tail of a distribution is on the right it is _____ skewed.

positively

If the tail of a distribution is on the left it is ____ skewed.

negatively

mode

the most frequently occurring score; easy to compare from frequency distribution.

median

the middle score in a distribution; less affected than the mean by a few deviant scores.

mean

the average; most commonly used central tendency measure.

range

lowest to highest score

average deviation

average distance from the mean

variance

average squared distance from the mean

standard deviation

square root of the variance

When is Pearson product-moment correlation used?

with interval or ratio data

When is Spearman rank-order correlation used?

when one variable is ordinal and the second is at least ordinal

When is Phi used?

when at least one variable is nominal

scatter plots

allow you to see the relationship of two variables and detects nonlinear relationships or correlations that are due to only a few outliers.

regression

using a correlation to predict one variable from knowing the score of the other variable; usually a linear (finding the best fitting straight line for the data); best illustrated in a scatter plot the the ___ line also plotted.

standard scores (z-scores)

a way to put scores on a common scale. tell us how much a certain score is above/below the mean. computed by subtracting the mean from the score and dividing the difference by the standard deviation.

inferential statistics

• used to draw inferences about populations on the basis of samples

• sometimes called “statistical tests”

• provide an objective way of quantifying the strength of the evidence for a hypothesis

If the null hypothesis is true but is rejected, what type of error was made?

Type 1 error

If the null hypothesis is false but is retained or failed to be rejected, what type of error was made?

Type 2 error

t-test

tests mean differences of two groups

analysis of variance

tests mean differences in two or more groups

power

sensitivity of the procedure to detect real differences between populations; a function of both the statistical test and the precision of the research design. increasing the sample size increases this.

effect size

indication that the size of the group differences is expressed in standard deviation units; is NOT affected by the size of the sample; large ones are easier to detect than small ones.

Descriptive statistics ______ the data

describe

Inferential statistics are used to draw _____ about population parameters on the basis of sample statistics

inferences

Generalization of research findings can occur only when:

What is observed in the research sample would also be observed in any other sample from the population.

Which type of research has the lowest level of constraint?

naturalistic observation

which type of research has the highest level of constraint?

experimental

unobtrusive observation

observing behavior without participant’s knowledge

participant observation

observing behavior while participating in the situation.

The purpose of control is to:

eliminate alternative explanations for results.

archival records

• exist independently of a research study

  • kept for purposes other than research

  • may be valuable in some studies

  • examples: gov’t records, school and hospital records, census data, etc…

• access to these may be restricted by legal and ethical constraints

studies can be replicated only if:

• the procedures are clearly specified

• the procedures were followed exactly

Ex Post Facto Fallacy

interpreting an observed contingency (correlation) as if it represented a causal connection. low-constraint observation will never provide the controls for such strong conclusions.

correlational research

quantifies the strength of the relationship among two or more variables (usually continuous). cannot prove a theory, but could negate a theory.

differential research

compares two or more preexisting groups (e.g., male and female difference studies); variables measured but not manipulated.

developmental research

assesses change over time

longitudinal research

• examining a variable over time; ex: brain development, product launches, long-term side effects of medicine.

• essentially time-series designs; single subjects are tested repeatedly.

• correlational in nature

cross-sectional research

• data is collected in one given time point across multiple samples

• can test many age groups simultaneously

• are faster

• but, cohort effects can be a problem.

• differential in nature

cohort effects

shared life experiences of people of a given age that lead them to behave similarly to others their age and different from people of other ages.

confounding variables

occurs when two variables vary together

• need to have them vary independently, usually by holding all but one variable constant

• failing to provide this control could result in artifactual findings (due to the failure to control ____)

comparing groups is reasonable only if we standardized he measurement procedures.

Differential is higher constraint because:

the researcher can select the comparison group(s) to control at least some of the potential confounding variables, thus providing stronger evidence for theory.

when to use correlational method

when we are interested in knowing the strength of a relationship for predictive purposes and often included to help interpret the primary findings of a study.

when to use differential research

when the manipulation of an independent variable is impractical, impossible, or unethical; we rely of comparing preexisting groups.

the larger your sample is, the more ______ it is of the population

representative

experimenter expectancy

researchers tending to see what they expect to see

experimenter reactivity

when researchers unconsciously influence participants

measurement reactivity

participants responding differently because they know they are being observed

which of the following is always used in differential research?

• random assignment of participants to groups

• the Pearson r or the Spearman r

• random selection of participants to ensure a representative sample

• groups differentiated on the basis of preexisting variables.

groups differentiated on the basis of preexisting variables.

how to control experimenter expectancy

use more objective measures whenever possible

how to control for experimenter reactivity

minimize experimenter contact with participants

how to control measurement reactivity

• use filler items to distract participants

• use unobtrusive measures when possible

• separate the measurements in time

moderator variable

a variable that seems to modify the relationship between other variables; acts upon the relationship between two variables and changes its direction or strength. (ex: gender, mental health status, medicine for kids but not adults)

coefficient of determination

indicates the proportion of variance accounted for

Example: How much of the variance of weight can be explained by height?

for a confound to be a confound it has to affect the scores on the _____ variable and the groups differ on this variable. (ex. attention spans could be a confound because attention affects memory.)

dependent