
alternative hypothesis
the prediction that there will be an effect (i.e. that your experimental manipulation will have an effect)

betweengroup design
another name for independent design

betweensubject design
another name for independent design

bimodal
a description of a distribution of observations that has two modes

binary variable
a categorical variable that has only two mutually exclusive categories (e.g. dead or alive)

boredom effect
refers to the possibility that performance in tasks may be influenced by boredom/lack of concentration if there are many tasks, or the task goes on for a long period.

categorical variable
any variable made up of categories of objects or entities

central tendency
a generic term describing the center of a frequency distribution of observations as measured by the mean, median, and mode

confounding variable
a variable (that may or may not have measured) other than the predictor variables in which we're interested than potentially affects an outcome variable

content validity
evidence that the content of a test corresponds to the content of the construct it was designed to cover

continuous variable
a variable that can be measured to any level of precision (values can exist within any two adjacent values)

correlational research
a form of research in which you observe what naturally goes on in the world without directly interfering with it. This term implies that data will be analyzed to look at relationships between naturally occurring variables rather than making statements about cause and effect. Compared with crosssectional and experimental research.

counterbalancing
a process of systematically varying the order in which experimental conditions are conducted. The aim is to remove systematic bias caused by practice effects or boredom effects.

criterion validity
evidence that scores from an instrument correspond with or predict concurrent external measures conceptually related to the measured construct

crosssectional research
a form of research in which you observe what naturally goes on in the world without directly interfering with it. Implies that the data come from people at different age points with different people representation each age point.

dependent variable
another name for outcome variable. This is associated with experimental methodology and is called because it is the variable that is not manipulated by the experimenter and so its value depends on the variables that have been manipulated.

discrete variable
 a variable that can only take on certain values (whole numbers) on the scale
 (very poor definition)

ecological validity
evidence that the results of a study, experiment or test can be applied, and allow inferences in realworld conditions

experimental hypothesis
synonym with alternative hypothesis

falsification
the act of disproving a hypothesis or theory

frequency distribution
a graph plotting values of observations on the horizontal axis, and the frequency with which each value occurs in the data set of the vertical axis

histogram
a frequency distribution (terrible definition)

hypothesis
a prediction about the state of the world

independent design
an experimental design in which different treatment conditions utilize different organisms and so the resulting data are independent (betweensubjects)

independent variable
another name for a predictor variable. This name is associated with experimental methodology because it is the variable that is manipulated by the experimenter and so its value does not depend on any other values.

interquartile range
the limits within which the middle 50% of an ordered set of observation falls, It is the difference between the value of the upper quartile and lower quartile

interval variable
data measured on a scale along the whole of which intervals are equal.

kurtosis
measurement of the degree to which scores cluster in the tails of a frequency distribution. A distribution with positive Kurtosis (leptokurtic) has too many scores in the tails and is too peaked, whereas a distribution with negative kurtosis (platykurtic) has too few scores in the tails and is quite flat.

leptokurtic
positive Kurtosis. Too many scores in the tails and is too peaked.

level of measurement
the relationship between what is being measured and the numbers obtained on a scale.

lower quartile
the value that cuts off the lowest 25% of the data. If the data are ordered and then divided into two halves at the median, then the lower quartile is the median of the lower half of the scores.

mean
a measurement of central tendency. A typical score (terrible definition)

measurement error
the discrepancy between the numbers used to represent the thing that we are measuring and the actual value of the thing we are measuring

median
the middle score of a set of ordered observations.

mode
the most frequently occurring score in a data set.

multimodal
a description of a distribution of observations that has more than two modes

negative skew
when a majority of the scores pile up on the right side of the distribution

nominal variable
variable where numbers merely represent names. Type of variable where the categories are by name only.

normal distribution
a probability distribution of a random variable that is known to have certain properties: perfectly symmetrical (skew of 0) and a kurtosis of 0.

null hypothesis
reverse of the experimental hypothesis. States that your prediction is wrong and the predicted effect does not exist.

ordinal variable
data that tell us not only those things have occurred, but also the order in which they occurred. Does not provide information about the differences between values.

outcome variable
a variable whose values we are trying to predict from one or more predictor variables

platykurtic
Has too few scores in the tails and is quite flat.

positive skew
a majority of the scores pile up on the left side of the distribution.

practice effect
refers to the possibility that participants' performance in a task may be influenced if they repeat the task because of familiarity with the experimental situation and/or the measures being used.

predictor variable
a variable that is used to try to predict values of another variable known as an outcome variable

probability distribution
a curve describing an idealized frequency distribution of a particular variable from which it is possible to ascertain the probability with which specific values of that variable will occur

qualitative methods
extrapolating evidence for a theory from what people say or write (or direct observation)

quantitative methods
inferring evidence for a theory through measurement of variables that produce numeric outcomes

quartile
generic term for the tree values that cut an ordered data set into for equal parts: lower quartile, the second quartile (median), and the upper quartile

randomization
the process of doing things in an unsystematic or random way. In experimental research, refers to random assignment of participants to different treatment conditions.

range
the range of scores is value of the smallest score subtracted from the highest score. It is a measure of the dispersion of a set of scores.

ratio variable
an interval variable but with the additional property that ratios are meaningful.

reliability
the ability of a measure to produce consistent results when the same entities are measured under different conditions.

repeatedmeasures design
an experimental design in which different treatment conditions utilize the same organisms and so the resulting data are related (haha organisms)

second quartile
another name for the median

skew
a measure of symmetry of a frequency distribution. Symmetrical distributions have a skew of 0. There are also negative and positive skews.

systematic variation
variation due to some genuine effect, either because of an experimenter doing something or natural variation between sets of variables.

tertium quid
the possibility that an apparent relationship between two variables is actually caused by the effect of a third variable on them both (called the thirdvariable problem)

testretest reliability
the ability of a measure to produce consistent results when the same entities are tested at two different points in time

theory
although it can be defined more formally, a theory is a hypothesized general principle or set of principles that explain known findings about a topic and from which new hypotheses can be generated.

unsystematic variation
variation that is not due to the effect in which we are interested but is due to natural differences between people. Variation that cannot be explained by whatever model we have fitted to the data.

validity
evidence that a study allows correct inferences about the question it was aimed to answer or that a test measures what it set out to measure conceptually

variables
anything that can be measured and can differ across entities across time

withinsubjects design
another name for a repeatedmeasures design

zscores
a value of an observation expressed in standard deviation units. Zscores distribution has mean of 0 and a standard deviation of 1.

