Statistics Lecture 3, 4, and 5

Standard score

a score derived from raw data and has a known basis for comparison

Percentiles

the distribution is divided into 100 equal parts with the mean at the 50 percentile

Quartile

the distribution is divided into 4 equal parts with the mean between the 2 & 3 quartile

Decile

the distribution is divided into 10 equal parts with the mean between the 5 & 6 decile

Variability

the spread or dispersion of a set of scores

What does it mean if the groups have a large amount of variance?

the difference between the means will have to be greater to find significance

Four measures of variability

range, variance, interquartile range, and standard deviation

Interquartile range

difference between the 75th and 25th percentile, ignores outliers and only considers 50 percent of the data

Variance

the distance of “X” from the mean, the distance is known as the deviation, the sum of the deviation will always equal zero

Standard deviation

the square root of the variance; a population statistic

Z score

a raw score expressed in standard deviation units

Standardizing data

transforming data into standard scores; useful in eliminating units of measurements

Skewness

a measure of symmetry or the lack of symmetry

Kurtosis

a measure of whether the data are peaked or flat relative to a normal distribution

Probability

the long-run proportion of a particular outcome

Percent between 0 and first SD

34%

Percent between first and second SD

13.5%

Percent between second and third SD

2.5%