research methods chapter 12

directionality problem

a correlational study does not determine which variable is the cause and which is the effect.

crierion and predictor variable

correlational studies often identify one variable as the predictor variable and the second variable as the criterion variable.

phi-coefficient.

If the Pearson correlation is computed for the coded data, the result is known as the

Researchers typically calculate a numerical value known as a

correlation, or a correlation coefficient

multiple regression concept

. The underlying concept is that one criterion variable such as academic performance can be explained or predicted from a set of predictor variables such as IQ and motivation.

The consistency

A correlation of +1.00 (or -1.00) indicates a perfectly consistent relationship, and a value of zero indicates no consistency whatsoever. Intermediate values indicate different degrees of consistency.

a monotonic relationship

A relationship that is consistently one-directional, either consistently positive or consistently negative

point-biserial correlation

If the non-numerical variable consists of exactly two categories, it is also possible to calculate a special correlation. First, the two categories are numerically coded as 0 and 1. For example, male 5 0 and female 5 1. The data then consist of two scores per person, an IQ score and a coded score for gender, and the Pearson correlation can be computed for the coded data.

Spearman correlation

If there is a consistent relationship between two variables so that Y tends to increase each time X increases, but not a linear relationship, then which correlation is designed to measure the consistency of the relations

Negative and positive slopes

In a scatter plot, a negative relationship is indicated by data points that cluster around a line that slopes down to the right. a positive slopes up to the right.

linear relationship

In most situations, researchers look for

Whats difficult?

In the behavioral sciences, the differences that exist from one individual to another tend to be large and are usually difficult to predict or explain.

third variable problem

It is always possible that a third (unidentified) variable is controlling the two variables and is responsible for producing the observed relation.

multiple regression

One commonly used technique for studying multivariate relationships is a statistical procedure known as

is to establish a relationship between variables that can be used for purposes of prediction.

One important use of correlational research

scatter plot

The data can be presented in a list showing the two scores for each individual or the scores can be shown in a graph known as

A correlation describes three characteristics of a relationship which are

The direction of the relationship,The form of the relationship, and The consistency or strength of the relationship.

A correlation, or correlation coefficient,

The sign of the correlation (1/-) indicates the direction of the relationship. The numerical value of the cor- relation (0.0 to 1.0) indicates the strength or consistency of the relationship. The type of correlation (Pearson or Spearman) indicates the form of the relationship.

the numerical value of the correlation

The strength or consistency of a relationship between variables is indicated by

independent-measures t test (for two groups) or an analysis of variance (for more than two groups).

The two groups are measured using

. The form of the relationship

Typically, researchers are looking for a pattern in the data that suggests a consistent and predictable relationship between the two variables.

what is the goal to find the equation that produces the most accurate?

Typically, the goal is to find the equation that produces the most accurate predictions of Y (the criterion variable) for each value of X (the predictor variable).

studying and amount of errors on a math test

Which of the following pairs of variables should produce a negative relationship?

goal of an experimental study is to demonstrate

a cause-and-effect relationship between two variables.

To establish the reliability of a measure, a researcher examines

a. the relationship between the scores from two administrations of the measure

, which ranges from 0.00 to 1.00, describes the consistency of the relationship with 1.00 (or -1.00) indicating a perfectly consistent relationship and 0.00 indicat- ing a complete lack of consistency.

both numerical and non-numerical data, the value of a correlation

ible for a relationship to be consistent and predictable,

but not linear

A researcher reports a positive relationship between sugar consumption and activity level for a group of 7-year-old children. Based on this relationship, which of the follow- ing conclusions is justified?

c. Children who consume more sugar tend to exhibit higher activity levels

correlational study usually does not produce

clear and unambiguous explanation for the relationship. In research terminology, correlational studies tend to have low internal validity

differential research strategy

establishes the existence of a relationship by demonstrating a difference between groups. Specifically, a differential design uses one of the two variables to define groups of participants and then measures the second variable to obtain scores within each group.

correlational study

examine and describe the associations and relationships between variables.

research terminology, correlational studies tend to have high

external validity

positive monotonic relationship

for example, increases in one variable tend to be accompanied by increases in the other variable. However, the amount of increase need not be con- stantly the same size.

The correlational design can

identify variables and describe relationships between variables that might suggest further investigation using the experimental strategy to determine cause-and-effect relationships.

coefficient of determination

is the squared value of a correlation and measures the percentage of variability in one variable that is determined, or predicted, by its relationship with the other variabl

A Pearson correlation

is used to describe and measure linear relationships when both variables are numerical scores from interval or ratio scales.

A Spearman correlation

is used to measure and describe monotonic relationships when both variables are ranks from an ordinal score or have been transformed to ranks

The benefit of a scatter plot is that

it allows you to see the charac- teristics of the relationship between the two variables.

If both variables are non-numerical, the relationship is typically evaluated by o

organizing the data in a matrix, with the categories of one variable forming the rows and the categories of the second variable forming the columns. Each cell of the matrix shows the frequency or number of individuals in that cell and the data are evaluated using a chi-square hypothesis test

regression

statistical process for using one variable to predict another is called

of the primary advantages of a correlational study is

that the researcher simply records what exists naturally. Because the researcher does not manipulate, control, or otherwise interfere with the variables being examined or with the surrounding environment, there is good reason to expect that the measurements and the relationships accurately reflect the natural events being examined.

The consistency or strength of the relationship.

the consistency of a relationship is typically measured and described by the numerical value obtained for a correlation coefficient.

correlational study views

the data as two scores, X and Y, for each individual, and looks for patterns within the pairs of scores to determine whether there is a relationship.

A researcher reports an inverse relationship between weight and exercise level for a group of 8-year-old children (greater weight is associated with less exercise). However, the researcher cannot be sure whether the extra weight is preventing the children from exercising or whether the lack of exercise is leading to greater weight. This is an example of

the directionality problem

If one of the scores is numerical, like IQ, and the other is non-numerical, like gender, the most common strategy is to use

the non-numerical variable to organize the scores into separate groups.

correlational research strategy is often used for

the preliminary work in an area that has not received a lot of research attention.

To establish the validity of a measure, a researcher examines

the relationship between the measure and another measure.

statistical significance of a correlation

the second important factor for interpreting the strength of a correlation. In the context of a correlation, the term significant means that a correlation found in the sample data is very un- likely to have been produced by random variation.

A researcher reports an inverse relationship between weight and exercise level for a group of 8-year-old children (greater weight is associated with less exercise). However, the researcher suspects that the children's rate of metabolism may be responsible for the relationship. That is, children with higher metabolism exercise more and weigh less than children with lower metabolism. This is an example of

the third-variable problem

The direction of the relationship

there is a clear tendency for individuals with larger X values to also have larger Y values. Equiva- lently, as the X values get smaller, the associated Y values also tend to get smaller. A relationship of this type is called a positive relationship.

two problems with correlational studies are

third variable, and the directionality problem

purpose of a correlational study

to establish that a relationship exists between variables and to describe the nature of the relationship.

Correlational research can be used for prediction,

to establish validity and reliability, and to evaluate theories. However, because of the third-variable and directionality problems, correlational research cannot be used to determine the causes of behavior

data for a correlational study consist of

two or more variables are measured to obtain a set of scores (usually two scores) for each individual. The measurements are then examined to identify any patterns of relationship that exist between the variables and to measure the strength of the relationship.