Statistical Methods for Psychology

Objectives

Must specify variables to be measured

What are the degrees of freedom for sample variance?

n - 1

A qualitative variable varies by

Class

Which variable is manipulated to create the groups？

Independent Variable

Which variable is measured in each group

Dependent Variable

What scale of measurement is the month of birth?

Nominal

A researcher records the levels of attraction for various fashion models among college students. He finds that mean levels of attraction are much higher than the median and mode for these data. (a) What is the shape of the distribution for the data described in this study? (b) Which measure of central tendency is most appropriate for describing these data? Explain.

Positively skewed distribution; the median is best because the data are positively skewed.

The mean is an appropriate measure for describing what types of data?

The mean is an appropriate measure for data that are normally distributed on an interval or ratio scale of measurement.

The mode is an appropriate measure for describing what types of data?

The mode is used with other measures of central tendency for any modal distribution and for nominal data.

A simple frequency distribution

can be used to summarize grouped data can be used to summarize ungrouped data summarizes the frequency of scores in a given category or range

In an experiment, researchers measure two types of variables:

independent and dependent variables

Procedures that allow researchers to infer or generalize observations made with samples to the larger population from which they were selected best describes descriptive or inferential statistics?

Inferential Statistics

State whether each of the following are continuous or discrete data. (a) time in seconds to memorize a list of words. (b) number of students in a statistics class. (c) the weight in pounds of newborn infants. (d) the SAT score among college students

(A) Continuous (B) Discrete (C) Continuous (D) Discrete

Based on the scale of measurement for each variable listed below, which measure of central tendency is most appropriate for describing the data? (a) the time (in years) it takes a sample of students to graduate college (b) the blood type (e.g., Type A, B, AB, O) of a group of participants (c) the rankings of college undergraduate academic programs

(A) mean (B) Mode (C) Median

To determine whether a new sleeping pill was effective, adult insomniacs received a pill (either real or fake), and their sleeping times were subsequently measured (in minutes) during an overnight observation period. Identify the 1. independent and 2. dependent variable in this study.

1. Sleeping pill (real or fake) 2. Time spent sleeping

Researchers often prefer to report cumulative percents from the bottom up to explain how certain scores rank at or below other scores in a distribution. What is this type of summary called?

A percentile rank

Statistics (Plural)

A structured and logical process of collecting, organizing, analyzing, interpreting, and presenting data based on specific objectives for the purpose of decision-making.

A quantitative variable varies by

Amount

The use of tables and graphs to summarize data is an example of descriptive or inferential statistics?

Descriptive statistics

A researcher records the number of hours (per week) that single mothers spend at work and states that the data are distributed normally. Which measure of central tendency is most appropriate for describing these data?

Mean

Is it appropriate to code month of birth data?

Yes it is appropriate to numerically code months because it is a nominal scale variable.