Chalter 3+4 Flashcards
Central tendency
The most typical, central, or common score of a variable
3 measures of central tendency
Mean
Median
Mode
Mode
Most common score
Median
Score of the middle case
Mean
Average score
Dispersion
Variety, diversity, or amount of variation between scores
Measures of dispersion
Index of qualitative variation
Range, interquartile range
Variance, standard deviation
Mind the median
10,10,8,7,5,4,2
7
Find the range
10,10,8,7,5,4,2
10-2=8
x̄
Mean
Calculate x̄
10,20,30,40,50
150 ➗5= 30
What scores does the mean use
All scores
What is a skewed distribution
Pulling the mean
Positive skewed distribution
Pulls the mean to the right
Mean> median
Negative skewed distribution
Pulls the mean to the left
Mean< median
Unskewed distribution
In the middle
Mean= median
Doesn’t happen in fact
Standard deviation
Average distance of each score to the mean
Variance
Square of standard deviation
3 characteristics of standard deviation
Use all score in a distribution
Lowest possible value is 0
Increase in value as distribution
How to find standard deviation (5)
- Subtract mean from each score
- Square each deviation
- Add squared deviations
- Divide the sum of squared deviations by the # of scores
- Find the square root of the result
Characteristics of the normal curve
-bell shape
-symmetrical/ unimodal
-theoretical
Units for z scores
Units of standard deviation
What level of measurement is used for z-scores
Interval ratio
2 characteristics of under the normal curve
Above or below a given score
Between two given scores
Where to look to find the area above and below z positive or negative
Example of a discrete variable
Rolling a die
Example of a continuous variable
Body weight
What is a normal curve
A bell shaped theoretical distribution of scores
What is probability
Ratio of number of success to number of possible events
Percentage between -1 & +1 SD
68.26
Percentage between -2 & +2 SD
95.44%
Percentage between -3 & +3 SD
99.72%
What is a Z-score
The way scores are expressed after they have been standardized to the theoretical normal curve
Index of qualitative variation
Amount of variation observed in a distribution of normal or ordinal-level variables scores to the maximum variation that could exist
outliers
Extreme high or low scores in a distribution
interquartile range
distance from the 3rd quartile to the 1st quartile
5 number summary
lowest score
highest score
median
1st quartile
3rd quartile
deviations
distance between the scores and mean
mean deviation
average of absolute deviations of the scores around the mean
coefficient of variation
ratio of SD to the mean
