Slide 2 KNR 445 Statistics t-tests Slide 1 Measures of Central
Tendency 1 Slide 3 Study note using audio slides Advantages
Revisiting them No attention lapses Nothing missed, everything
available for comprehensive study guide come exam times More class
time available for discussion/group work/explanation/SPSS
Disadvantage Not real time lecture/no immediate interaction
w/instructor Can result in wanting to ask questions, but not being
able to Recommendation: Print slides before listening, make notes
and write questions down as you go Email question/s if needed in
order to make progress Listen to the slides early in the week so
that theres plenty of time to allow for communication with the
instructor KNR 445 CT/Spread & Z-scores Slide 2 1 2 3 4 Slide 4
KNR 445 CT/Spread & Z-scores Slide 3 Measure of Central
Tendency What SINGLE summary statistic or parameter best describes
the central location of an entire distribution? Mode: which value
occurs most (what is fashionable) Median: the middle value in the
data, once its ranked (the 50th percentile) Mean: mathematical
balance point; arithmetic mean; mathematical mean 1 2 3 4 General
note on this early stuff Slide 5 KNR 445 CT/Spread & Z-scores
Slide 4 Mode Most frequent occurrence What if data were 17, 19, 20,
20, 22, 23, 23, 28 Problem: set of numbers can be bimodal, or
trimodal, depending on the scores Not a stable measure 1 2 3 Slide
6 KNR 445 CT/Spread & Z-scores Slide 5 Median Rank numbers,
pick middle one What if data were 17, 19, 20, 23, 23, 28 Solution:
add up two middle scores, divide by 2 (=21.5) Best measure in
asymmetrical distribution (ie skewed), not sensitive to extreme
scores 1 2 Slide 7 KNR 445 CT/Spread & Z-scores Slide 6 Mean
Add up the numbers and divide by the sample size (number of
numbers!) Try this one 5,3,2,6,9 This is the best measure of the
three after all, it uses more information than any of the others 1
2 3 Slide 8 KNR 445 CT/Spread & Z-scores Slide 7
Characteristics of the Mean Balance point point around which
deviations sum to zero Deviation is difference between two numbers
For instance, if scores are 5,3,2,6,9 Mean is 5 Sum of deviations:
0+(-2)+(-3)+1+4 = 0 See? 1 Slide 9 KNR 445 CT/Spread & Z-scores
Slide 8 Characteristics of the Mean Balance point Affected by
extreme scores Scores 7, 11, 11, 14, 17 Mean = 12, Mode and Median
= 11 Scores 7, 11, 11, 14, 170 Mean = 42.6, Mode & Median = 11
1 Slide 10 KNR 445 CT/Spread & Z-scores Slide 9 Characteristics
of the Mean Balance point Affected by extreme scores Appropriate
for use with interval or ratio scales of measurement 1 Slide 11 KNR
445 CT/Spread & Z-scores Slide 10 Characteristics of the Mean
Balance point Affected by extreme scores Appropriate for use with
interval or ratio scales of measurement More stable than Median or
Mode when multiple samples drawn from the same population Basis for
inferential stats 1 Slide 12 KNR 445 CT/Spread & Z-scores Slide
11 Guidelines to choose Measure of Central Tendency Mean is
preferred because it is the basis of inferential statistics Median
may be better for skewed data? Distribution of wealth in the US
Mode to describe average of nominal data (Percentage - relative
frequency) 1 Slide 13 KNR 445 CT/Spread & Z-scores Slide 12
Median Mode Mean Scores Normal Distribution 1 2 3 4 Slide 14 KNR
445 CT/Spread & Z-scores Slide 13 Positively skewed
distribution Scores Median Mode Mean 1 2 Slide 15 KNR 445 CT/Spread
& Z-scores Slide 14 Negatively skewed distribution Median Mode
Mean Scores 1 2 Slide 16 End of filevariability next. KNR 445
CT/Spread & Z-scores Slide 15
