chapter 3 Flashcards
Deciles.
The points that divide a distribution of scores into 10ths.
Mean
The arithmetic average of the scores. represents the mean of a sample, and m, the mean of a population.
Measures of central tendency.
Statistics that summarize a distribution of scores by reporting the most typical or representative value of the distribution.
Median
The point in a distribution of scores above and below which exactly half of the cases fall.
Mode
The most common value in a distribution or the largest category of a variable.
Percentile
A point below which a specific percentage of the cases fall
Quartiles
The points that divide a distribution into quarters.
(uppercase Greek letter sigma)
“The summation of.”
Skew
The extent to which a distribution of scores has a few scores that are extremely high A>- (positive skew) or extremely low -<A (negative skew).
Xi (“X-sub-i ”).
Any score in a distribution.
the purpose of the measure of central tendencies
Each reports some information about the most typical or representative value in a distribution. Appropriate use of these statistics permits the researcher to report important information about an entire distribution of scores in a single, easily understood number.
the mode on variables
reports the most common score and is used most appropriatly with nominally measured variable
the median on report
report the score theat is the exact center of the distribution, –> ordinal level & interval ratio
the mean
interval ratio
the mean when the distribution is skewed
the mean is affected by every scores numeric outcome unlike the mode and the median
when positively skewed ( extreme high scores - A>- ) the mean always be greater than the mean
when negatively skewed -<A ( the mean will be lowed in the value than the median )
the most appropriate way to measure of central tendency of each level of measurement
nominal - ordinal - interval & ratio
nominal –>mode
ordinal –> median
interval & ratio –> mean
use the mode when
- The variable is measured at the nominal level. 2. You want a quick and easy measure for ordinal and interval-ratio variables. 3. You want to report the most common score.
use the median when
- The variable is measured at the ordinal level. 2. A variables measured at the interval-ratio level has a highly skewed distribution. 3. You want to report the central score. The median always lies at the exact center of a distribution.
use the mean when
- The variable is measured at the interval-ratio level (except when the variable is highly skewed). 2. You want to report the typical score. The mean is “the fulcrum that exactly balances all of the scores.” 3. You anticipate additional statistical analysis.
