Descriptive Statistics (Measures of Central Tendency and Shapes of Distribution) Flashcards
typical or most representative value of a group of scores; Mean, Median, Mode
Central Tendency
arithmetic average of a group of scores; sum of the scores divided by the number of scores; the balance point of a distribution
Mean (M)
μ
population mean
M
sample mean
an average in which each observation in the data set is assigned or multiplied by a weight before summing to a single average value
Weighted Mean
Characteristics of the Mean
- Changing a score in the distribution can affect the value of the mean
- Introducing a new score or removing a score can affect the value of the mean.
- Adding or subtracting a constant from each score will change the value of the mean.
- Multiplying or dividing each score by a constant will change the value of the mean
When to use the Mean?
- quantitative research, especially in psychological studies
- approximately normally distributed data
- with equal-interval variables: (Continuous Data/Variable &
Interval/Ratio)
middle score when all the scores in a distribution are arranged from lowest to highest
Median (Mdn)
When to use the Median?
- with rank-ordered variables
- non-normal or skewed distributions
- when a distribution has one or more outliers
- rarely used in psychology research
score with an extreme (very high or very low) in relation to the other scores in the distribution.
outliers
value with the greatest frequency in the distribution
mode
When to use the Mode?
- with categorical variables (nominal)
- rarely used in psychology research
frequency distribution with one value clearly having a larger frequency than any other
Unimodal Distribution
frequency distribution with two approximately equal frequencies, each clearly larger than any the others
Bimodal Distribution
frequency distribution with two or more high frequencies separated by a lower frequency
Multimodal Distribution
frequency distribution in which all values have approximately the same frequency
Rectangular Distribution
distribution in which the pattern of frequencies on the left and right side are mirror images of each other
Symmetrical Distribution
distribution in which the scores pile up on one side of the middle and are spread out on the other side; distribution that is not symmetrical
Skewed Distribution
the peak (highest frequency) in the distribution is on the left-hand side with tail tapering off the right
Positively Skewed Distribution
a situation in which many scores pile up at the low end of a distribution (creating a skewness to the right) because it is not possible to have any lower score.
Floor Effect
the peak (highest frequency) in the distribution is on the right-hand side with the tail tapering of the left
Negatively Skewed Distribution
a situation in which many scores pile up at the high end of a distribution (creating a skewness to the left) because it is not possible to have a higher score.
Ceiling Effect
specific, mathematically defined, bell-shaped frequency distribution that is symmetrical and unimodal; distributions observed in nature and in research commonly approximates it
Normal Curve
extent to which a frequency distribution deviates from a normal curve in terms of whether its curve in the middle is more peaked or flat than the normal curve.
Kurtosis
the scores are concentrated towards the mean
Leptokurtic
normal curve
Mesokurtic
the scores have an extremely large deviation from the mean
Platykurtic
