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Quiz 1
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Gravity
Key Concepts:
Terms in this set (46)
statistics
branch of mathematics that focuses on the organization, analysis, and interpretation of a group of numbers
descriptive statistics
procedures for summarizing a group of scores or otherwise making them more understandable
inferential statistics
procedures for drawing conclusions based on the scores collected in a research study but going beyond them
variable
characteristic that can have different values
value
possible number or category that a score can have
score
particular person's value on a variable
numeric variable
variable whose values are numbers (as opposed to a nominal variable). Also called quantitative variable.
equal-interval variable
variable in which the numbers stand for approximately equal amounts of what is being measured
ratio scale
an equal-interval variable is measured on a ratio scale if it has an absolute zero point, meaning that the value of zero on the variable indicates a complete absence of the variable
rank-order variable
numeric variable in which the values are ranks, such as class standing or place finished in a race. Also called ordinal variable
nominal variable
variable with values that are categories (that is, they are names rather than numbers). Also called categorical variable
levels of measurement
types of underlying numerical information provided by a measure, such as equal-interval, rank-order, and nominal (categorical
discrete variable
variable that has specific values and that cannot have values between these specific values
continuous variable
variable for which, in theory, there are an infinite number of values between any two value
central tendency
typical or most representative value of a group of scores
mean
arithmetic average of a group of scores; sum of the scores divided by the number of scores
mode
value with the greatest frequency in a distribution
median
middle score when all the scores in a distribution are arranged from lowest to highest
variance
measure of how spread out a set of scores are; average of the squared deviations from the mean
standard deviation
square root of the average of the squared deviations from the mean; the most common descriptive statistic for variation; approximately the average amount that scores in a distribution vary from the mean
z-score
number of standard deviations that a score is above (or below, if it is negative) the mean of its distribution; it is thus an ordinary score transformed so that it better describes the score's location in a distribution
raw score
ordinary score (or any number in a distribution before it has been made into a Z score or otherwise transformed)
0
the mean of any distribution of z-scores
1
the standard deviation of any distribution of z-scores
normal distribution
ordinary score (or any number in a distribution before it has been made into a Z score or otherwise transformed); standard deviation percentages 2%, 14%, 34%
population
entire group of people to which a researcher intends the results of a study to apply; larger group to which inferences are made on the basis of the particular set of people (sample) studied
sample
scores of the particular group of people studied; usually considered to be representative of the scores in some larger population
random selection
method for selecting a sample that uses truly random procedures (usually meaning that each person in the population has an equal chance of being selected); one procedure is for the researcher to begin with a complete list of all the people in the population and select a group of them to study using a table of random numbers
population parameter
actual value of the mean, standard deviation, and so on, for the population; usually population parameters are not known, though often they are estimated based on information in samples
sample statistics
descriptive statistics, such as the mean or standard deviation, figured from the scores in a group of people studied
standard error
standard deviation of a distribution of means square root of the variance of a distribution of means
confidence interval
roughly speaking, the range of scores (that is, the scores between an upper and lower value) that is likely to include the true population mean; more precisely, the range of possible population means from which it is not highly unlikely that you could have obtained your sample mean
correlation
association between scores on two variables
scatter plot
graph showing the relationship between two variables: the values of one variable are along the horizontal axis and the values of the other variable are along the vertical axis; each score is shown as a dot in this two-dimensional space
positive correlation
relation between two variables in which high scores on one go with high scores on the other, mediums with mediums, and lows with lows; on a scatter diagram, the dots roughly follow a straight line sloping up and to the right
negative correlation
relation between two variables in which high scores on one go with low scores on the other, mediums with mediums, and lows with highs; on a scatter diagram, the dots roughly follow a straight line sloping down and to the right
zero correlation
no systematic relationship between two variables
restriction in range
situation in which you figure a correlation but only a limited range of the possible values on one of the variables is included in the group studied
correlation matrix
common way of reporting the correlation coefficients among several variables in a research article; table in which the variables are named on the top and along the side and the correlations among them are all shown
predictor variable
in prediction, variable that is used to predict scores of individuals on another variable
criterion variable
in prediction, a variable that is predicted
linear prediction rule
formula for making predictions; that is, formula for predicting a person's score on a criterion variable based on the person's score on one or more predictor variables
regression line
line on a graph such as a scatter diagram showing the predicted value of the criterion variable for each value of the predictor variable; visual display of the linear prediction rule
slope
steepness of the angle of a regression line in a graph of the relation of scores on a predictor variable and predicted scores on a criterion variable; number of units the line goes up for every unit it goes across
intercept
the point where the regression line crosses the vertical axis; the regression constant (a).
error
in prediction, the difference between a person's predicted score on the criterion variable and the person's actual score on the criterion variable
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