12.2 Descriptive Statistics Flashcards
Two statistics are needed to describe the data. A single number can be used to describe the ____ ____, or how participants scored over all. Another number describes the ____, or how widely the distribution of scores is spread.
central tendency, variability
____ statistics allow researchers to make precise statements about the data.
Descriptive
A ____ ____ statistic tells us what the sample as a whole, or on the average, is like.
central tendency
There are three measures of central tendency – the ____, the ____, and the ____.
mean, median, mode
The ____ of a set of scores is obtained by adding all the scores and dividing by the number of scores. It is symbolised as x bar or M.
mean
The Greek letter ∑ (____) is statistical notation for summing a set of numbers.
sigma
The ____ is the score of that divides the group in half (with 50% scoring below and 50% scoring above the median). In scientific reports, the median is abbreviated as Mdn.
median
The ____ is the most frequent score. The mode is the only measure of central tendency that is appropriate if a nominal scale is used.
mode
A measure of ____ is a number that characterises the amount of spread in a distribution of scores.
variability
The ____ ____, symbolised as s, indicates the average deviation of scores from the mean. In scientific reports, it is abbreviated as SD.
standard deviation
The standard deviation is derived by first calculating the ____, symbolised as s² (the standard deviation is the square root of the variance).
variance
The standard deviation of a set of scores is ____ when people have similar scores close to the mean. The standard deviation becomes ____ as more people have scores that lie farther from the mean value.
Small, larger
Another measure of variability is the ____, which is simply the difference between the highest score and the lowest score.
range
A ____ ____ is a statistic that describes how strongly variables are related to one another.
correlation coefficient
One familiar correlation coefficient is the ____ ____-____ correlation coefficient, which is used when both variables have interval or ratio scale properties.
Pearson product-moment
The Pearson product-moment correlation coefficient is called the ____ _. Values of a Pearson r can range from 0.00 to ±1.00.
Pearson r
A correlation of ___ indicates there is no relationship between the variables. The nearer a correlation is to ___ (plus or minus), the stronger is the relationship.
0.00, 1.00
The sign of the Pearson r tells us about the ____ of the relationship; that is, whether there is a positive relationship or a negative relationship between the variables.
direction
To calculate a correlation coefficient, we need to obtain ____ of observations from each subject.
pairs
The Pearson r is designed to detect only linear relationships. If the relationship is ____ the correlation coefficient will not indicate the existence of a relationship.
curvilinear
____ ____ refers to the strength of association between the variables. The Pearson r correlation coefficient is one indicator of effect size; it indicates the strength of the linear association between two variables.
Effect size
As with all correlation coefficients, the values of the effect size correlation can range from ___ to ___.
0.00 to 1.00
The advantage of reporting effect size is it provides us with a scale of values that is ____ across all types of studies.
consistent
A general guide is it correlations near .15 are considered ____, those near .30 are ____, and correlations above .40 are ____.
small, medium, large.
It is sometimes preferable to report the squared value of a correlation coefficient; instead of r, you will see r². This transformation changes r to a ____.
percentage
The r² value is sometimes referred to as ____ of ____ ____ between two variables.
percent of shared variance
____ ____ are calculations used to predict a person’s to score on one variable when that person’s score on another variable is already known.
Regression equations
The general form of a regression equation is Y = a + bX
Where Y is the score we wish to predict, X is the known score, a is a constant, and b is a weighting adjustment factor that is multiplied by X (it is the slope of the line created with this equation).
When researchers are interested in predicting some future behaviour (called a ____ variable) on the basis of a person’s score on some other variable (called the ____ variable), is this necessary to demonstrate that there is a high correlation between the criterion and predictor variables.
criterion variable, predictor variable
A technique called ____ ____ is used to combine a number of predictor variables to increase the accuracy of prediction of a given criterion or outcome variable.
multiple correlation
A multiple correlation, symbolised as R, is the correlation between a ____ set of predictor variables and a single criterion variable.
combined
Taking all of the predictor variables into account usually permits greater ____ of ____ than if any single predictor is considered alone.
accuracy of prediction
A multiple regression equation can be calculated that takes the following form: Y = a + b₁X₁ + b₂X₂ + bnXn ….
Where Y is the criterion variable, X₁ to Xn are the predictive variables, a is the constant, and b₁ to bn are weights that are multiplied by scores on the predictor variables.
Researchers face of the ____-____ ____ in nonexperimental research when some uncontrolled third variable maybe responsible for the relationship between the two variables of interest.
third-variable problem
A technique called ____ ____ provides a way of statistically controlling third variables.
partial correlation
A partial correlation is a correlation between the two variables of interest, with the influence of the ____ ____ removed from, or “partialed out of”, the original correlation.
third variable
This provides an ____ of what the correlation between the primary variables would be if the third variable were held constant. This is not the same is actually keeping the variable constant, but it is a useful approximation.
indication
To ____ a partial correlation, you need to have scores on the two primary variables of interest and the third variable that you want to examine.
calculate
