Central Tendency >Mean: arithmetic average Add up all
scores, divide by number of scores >Median: middle score
>Mode: most common score
Slide 3
Calculating the Mean >Add up all scores >Divide by number
of scores
Slide 4
Calculating the Median >Line up the scores in ascending
order >Find the middle number For an odd number of scores, just
find the middle value. For an even number of scores, divide number
of scores by two. Take the average of the scores around this
position.
Slide 5
Calculating the Mode >Line up the scores in ascending order.
>Find the most frequent score. >Thats the Mode!
Slide 6
>Do measures of central tendency capture the following slide
adequately?
Slide 7
Figure 4-4: Bipolar Disorder and the Modal Mood
Slide 8
>An early lesson in lying with statistics Which central
tendency is best: mean, median, or mode? Outliers and the Mean
Slide 9
Figure 4-6: The Mean without the Outlier
Slide 10
Which Measure of Central Tendency is the Best? >The mean is
most commonly used best for symmetric distributions >The median
is best for a skewed distribution or one with outlier(s), >The
mode is used in 3 cases: One particular score dominates a
distribution Distribution is bimodal or multimodal Data are
nominal
Slide 11
Measures of Variability >Range From the lowest to the
highest score >Variance Average square deviation from the mean
>Standard deviation Variation from the sample mean
Slide 12
Calculating the Range >Determine the highest score
>Determine the lowest score >Subtract the lowest score from
the highest score
Slide 13
>Subtract the mean from each score >Square every
deviation from the mean >Sum the squared deviations >Divide
the sum of squares by N Calculating the Variance
Slide 14
>Typical amount the scores vary or deviate from the sample
mean This is the square root of variance Calculating the Standard
Deviation
Slide 15
Practice Problem >Age of Classmates? Calculate the mean,
median, mode, standard deviation, and the variance for the age of
the members of your class.
Slide 16
Interquartile Range >Measure of the distance between the 1
st and 3 rd quartiles. >1 st quartile: 25th percentile of a data
set >The median marks the 50th percentile of a data set. >3
rd quartile: marks the 75 th percentile of a data set
Slide 17
Calculating the Interquartile Range Countries top finishes in
the World Cup omitting countries with a score of 0 1, 1, 2, 2, 2,
2, 2, 2, 2, 2, 4, 6, 8, 10