PSYC 2260 Study Guide - Winter 2018, Comprehensive Midterm Notes - Normal Distribution, Variance, Null Hypothesis
12 Oct 2018
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PSYC 2260
MIDTERM EXAM
STUDY GUIDE
Fall 2018
PSYC 2260 Introduction to Research Methods in Psychology
Chapter 1 Displaying Order
2 Branches of Statistics:
1. Descriptive: to summarize and describe order, pattern, or structure in a group of number
2. Inferential: drawing conclusion based on the numbers but used to infer beyond the number
Basic terms and concepts:
Variable Value score
Self-esteem Value of 1 to 10 His score is 6
1. Nominal (categorical)
- Number represent discrete qualitative categories (1= female; 2=male)
2. Numeric (quantitative)
-Rank-order (ordinal): 1=strongly disagree…..5=strongly agree; place finished in a race
-Equal-interval: number represents equal amounts of what is being measured. E.g. height in
inches; speed in km/h
-Ratio scale: an equal-interval variable; has an absolute zero point
-Discrete variable: variable that has specific values and that cannot have values between
these specific values
-Continuous variables: “underling continuity” when an infinite number of possible value
exists between any 2 measured value:
E.g. self-esteem 1 2 3 4 5 ; You can have 1.1, 1.2, 1.3….
True scales(ratio scale) are not used that much in psychology, most psychological variables are
in nominal; rank-ordered, equal-interval
Note: a variable can have several different characteristics
- E.g. Gender: both nominal and discrete
Age: is continuous, equal-interval, and a ratio scale
Stress: on a scale of 1-7 is discretely measured, but could also be continuous
Frequency of values:
How many times a value occurs in a variables
find more resources at oneclass.com
find more resources at oneclass.com
PSYC 2260 Introduction to Research Methods in Psychology
Important to know as frequency of value determines the shape of distribution
Shape determines or limits the kinds of statically analysis that can be done
Ways of Looking at frequency:
1. Frequency Table (a ‘tally’ of score): use interval; low end of interval is a multiple of the interval
size; E.g. interval size=10; low ends are 0, 10, 20, 30, 40
2. Frequency Graph (visual display)
- Frequency Polygram (line graph)/ Histogram: has 2 extra values, one below and one above
the range to “close” the shape
Shape of Distributions
A) Modality
- “Uni-moda” = singe peak
- “Bi-model” = 2 peaks
- “Rectangular” = fairly flat, no peaks
B) Symmetry and Skew
-Symmetrical Distribution: values are almost “balanced” on either side distribution
-Skewed Distribution: distribution of data that is not symmetrical around the midpoint
-Positive skew: fewer score on the right-hand side, result in a longer tail on the right
Could be due to “floor effect” (lower score not possible)
-Negative skew: fewer score on the left-hand side, result in a longer tail on the left
Could be due to a “ceiling effect” (higher scores not possible)
C) Normality and Kurtosis
- The normal curve (bell-shaped) is the standard of comparison
-Kurtosis: how much the shape of the distribution is different from the “normal curve”
E.g. a flatter distribution with heavy tails (more scores in the tails) is called
“platykurtic”
E.g. a skinny distribution with “light” tails (fewer scores in the tails) is called
“leptokurtic”
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
2 branches of statistics: descriptive: to summarize and describe order, pattern, or structure in a group of number. Inferential: drawing conclusion based on the numbers but used to infer beyond the number. Number represent discrete qualitative categories (1= female; 2=male: numeric (quantitative) Rank-order (ordinal): 1=strongly disagree 5=strongly agree; place finished in a race. Equal-interval: number represents equal amounts of what is being measured. Ratio scale: an equal-interval variable; has an absolute zero point. Discrete variable: variable that has specific values and that cannot have values between these specific values. Continuous variables: underling continuity when an infinite number of possible value exists between any 2 measured value: E. g. self-esteem 1 2 3 4 5 ; you can have 1. 1, 1. 2, 1. 3 . True scales(ratio scale) are not used that much in psychology, most psychological variables are in nominal; rank-ordered, equal-interval. Note: a variable can have several different characteristics. Age: is continuous, equal-interval, and a ratio scale.
