Essentials of Statistics for the Behavioral Sciences Ch.3
Unlike mean & median, what can there be more than 1 of?
Mode
What is the only measure of central tendency that is always an actual score from your data set?
Mode
What is least & most affected by outliers?
Mode & Mean
Mean (pg. 61)
Calculated by adding up all the scores in the distribution & dividing by the number of scores. -average
Weighted Mean (pg. 64)
Combined mean of 2 separate set of scores, calculated by adding up all the scores from BOTH data sets & divide by the total number of scores in BOTH data sets.
When would adding/removing NOT change the mean?
If the score was exactly equal to the mean.
Outliers
In skewed distributions, it's the extreme values in the tail
What will happen if the value of any score is changed?
It will change the mean.
Weighted Mean (Formula) (pg. 64)
M = (∑X1 + ∑X2) / (n1 + n2) *note that this is for a sample
Sample Mean (Formula)
M = ∑X/ n
What are 3 kinds of central tendency?
Mean, Median & Mode
Central Tendency (General Term)
Single value that accurately describes the center of the distribution & represents the entire distribution of scores. (Aka "the average")
Central Tendency
Statistical measure that attempts to determine the single value/ how a data set/collection of scores can be summarized using a single number.
What if there was an even number of scores?
Take the mean of the middle 2 scores.
Symmetrical Distribution (pg. 80)
The right hand side of the graph is a mirror image of the left hand side
Mode (pg. 73)
The score/tendency that has the greatest frequency/ most occurring score. -use the mode with nominal scales, discrete variables, describing shape
Median (pg. 69)
When the scores in a distribution are listed in order of smallest-largest, the median is the midpoint of the list.
Skewed Distributions (pg.81)
especially distributions for continuous variables, there is a strong tendency for the mean, median, and mode to be located in different positions
Mean as a balance point
the mean can never be outside the range of scores
Population Mean (Formula)
μ = ∑X / N
