12.2 Descriptive Statistics

Question 0

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.

Answer 0

central tendency, variability

Question 1

____ statistics allow researchers to make precise statements about the data.

Answer 1

Descriptive

Question 2

A ____ ____ statistic tells us what the sample as a whole, or on the average, is like.

Answer 2

central tendency

Question 3

There are three measures of central tendency – the ____, the ____, and the ____.

Answer 3

mean, median, mode

Question 5

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.

Answer 5

mean

Question 6

The Greek letter ∑ (____) is statistical notation for summing a set of numbers.

Answer 6

sigma

Question 7

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.

Answer 7

median

Question 8

The ____ is the most frequent score. The mode is the only measure of central tendency that is appropriate if a nominal scale is used.

Answer 8

mode

Question 9

A measure of ____ is a number that characterises the amount of spread in a distribution of scores.

Answer 9

variability

Question 10

The ____ ____, symbolised as s, indicates the average deviation of scores from the mean. In scientific reports, it is abbreviated as SD.

Answer 10

standard deviation

Question 11

The standard deviation is derived by first calculating the ____, symbolised as s² (the standard deviation is the square root of the variance).

Answer 11

variance

Question 12

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.

Answer 12

Small, larger

Question 13

Another measure of variability is the ____, which is simply the difference between the highest score and the lowest score.

Answer 13

range

Question 14

A ____ ____ is a statistic that describes how strongly variables are related to one another.

Answer 14

correlation coefficient

Question 15

One familiar correlation coefficient is the ____ ____-____ correlation coefficient, which is used when both variables have interval or ratio scale properties.

Answer 15

Pearson product-moment

Question 16

The Pearson product-moment correlation coefficient is called the ____ _. Values of a Pearson r can range from 0.00 to ±1.00.

Answer 16

Pearson r

Question 17

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.

Answer 17

0.00, 1.00

Question 18

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.

Answer 18

direction

Question 19

To calculate a correlation coefficient, we need to obtain ____ of observations from each subject.

Answer 19

pairs

Question 20

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.

Answer 20

curvilinear

Question 21

____ ____ 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.

Answer 21

Effect size

Question 22

As with all correlation coefficients, the values of the effect size correlation can range from ___ to ___.

Answer 22

0.00 to 1.00

Question 23

The advantage of reporting effect size is it provides us with a scale of values that is ____ across all types of studies.

Answer 23

consistent

Question 24

A general guide is it correlations near .15 are considered ____, those near .30 are ____, and correlations above .40 are ____.

Answer 24

small, medium, large.

Question 25

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 ____.

Answer 25

percentage

Question 26

The r² value is sometimes referred to as ____ of ____ ____ between two variables.

Answer 26

percent of shared variance

Question 27

____ ____ are calculations used to predict a person’s to score on one variable when that person’s score on another variable is already known.

Answer 27

Regression equations

Question 28

The general form of a regression equation is Y = a + bX

Answer 28

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).

Question 29

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.

Answer 29

criterion variable, predictor variable

Question 30

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.

Answer 30

multiple correlation

Question 31

A multiple correlation, symbolised as R, is the correlation between a ____ set of predictor variables and a single criterion variable.

Answer 31

combined

Question 32

Taking all of the predictor variables into account usually permits greater ____ of ____ than if any single predictor is considered alone.

Answer 32

accuracy of prediction

Question 33

A multiple regression equation can be calculated that takes the following form: Y = a + b₁X₁ + b₂X₂ + bnXn ….

Answer 33

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.

Question 34

Researchers face of the ____-____ ____ in nonexperimental research when some uncontrolled third variable maybe responsible for the relationship between the two variables of interest.

Answer 34

third-variable problem

Question 35

A technique called ____ ____ provides a way of statistically controlling third variables.

Answer 35

partial correlation

Question 36

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.

Answer 36

third variable

Question 37

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.

Answer 37

indication

Question 38

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.

Answer 38

calculate