PSY 2400 Exam 1 Study Guide
Concepts to know:
 What are descriptive statistics?
o Statistical procedures used to summarize, organize, and simplify data
 What are inferential statistics?
o Consist of techniques that allow us to study samples and then make
generalizations about the populations from which they were selected
 What are the symbols we have learned for statistical concepts so far?
 How is the order of operations used in statistics?
o PEMDAS
 What are parametric statistics?
o Tests that concern parameters and require assumptions about parameters
 Why should my sample look like a theoretical population?
o To describe characteristics of the population as a whole not just a group of the
population
 What is a biased sample?
o Average value of the statistic either underestimates or overestimates the
corresponding population parameter
 How is variability related to the normal distribution?
o Standard deviation is the square root of the variance which is a useful measure of
variability when the distribution is normal
 Why do we need some variability in our data?
o Gives you a way to describe how much data sets vary and allows you to use
statistics to compare your data to other sets of data
 What is a statistical model?
o Mathematical model that embodies a set of statistical assumptions concerning the
generation of sample data. Used between one or more random variables and other
non-random variables
 How is variability related to the concept of a statistical model?
 How do the scales of measurement related to the overall concept of conducting statistical
analyses?
 Why do we have to square all the deviation scores and what is this value called?
Definitions:
 Quantitative methods
 Qualitative methods
 Statistics (definition)
o Refers to a set of mathematical procedures for organizing, summarizing, and
interpreting information
 Population
o Set of all individuals of interest in a particular study
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Sample
o set of individuals selected from a population, usually intended to represent the
population in a research study
Continuous data
o There are an infinite number of possible values that fall between any two
observed values. divisible into an infinite number of fractional parts.
Categorical data
Frequency distribution
o An organized tabulation of the number of individuals located in each category on
the scale of measurement
Histogram
Central tendency: mean, median, mode
o Statistical measure to determine a score that defines the center of a distribution.
Used to find the single score that is most typical of the entire group
Skew
Kurtosis
Variability: range, sum of squared errors, variance, standard deviation
o Provides a quantitative measure of differences between scores in a distribution
and describes the degree to which the scores are spread out or clustered together
Deviation score
o Difference between a score and the mean, and is calculated as deviation=X-μ
Degrees of freedom
o Degrees of freedom describe the number of scores in a sample that are
independent and free to vary. Because the sample mean places a restriction on the
value of one score in the sample, there are n-1 degrees of freedom for a sample
with n scores
Practice Problems:
An athletics coach examines his own players on how quickly they can each run a 100-meter
dash. This data are below:
Player
1
Seconds .14
2
.16
3
.18
4
.14
5
.13
6
.13
7
.12
8
.14
9
.16
10
.16
1. Calculate the measures of central tendency – mean, median, mode.
2. Calculate the measures of variability – sum of squared errors, variance, and standard
deviation.
Stillman, Baumeister, and DeWall (2007) conducted a study where participants listened to a
variety of jokes. To determine how funny the jokes were, the researchers asked a group of 86
undergraduate students to rate the jokes on a scale from 1 (very unfunny) to 21 (very funny).
Participants rated a “lawyer joke” as one of the funniest jokes with a rating average of 14.48 (σ =
4.38).
1. What is the dependent variable and what is the level of measurement?