Lecture 5A: Descriptive Statistics Flashcards
What is the purpose of descriptive statistics?
Provide a description of the sample without generalizing beyond it
What are the three measures of central tendency?
- Mode
- Median
- Mean
What is the mode?
The score or observation that occurs most frequently
What is the median?
The middle value that divides the dataset into two equal halves
What is the mean?
The average of a set of values
What are the measures of variability/dispersion?
- Range
- Interquartile range (IQR)
- Variance
- Standard Deviation (SD)
- Coefficient of Variation (CV)
What does the range represent?
The difference between the largest and smallest scores
What is the interquartile range (IQR)?
The difference between the first quartile (Q1) and the third quartile (Q3)
What is variance?
The (sum of squared deviations from the mean) divided by the (number of cases minus one)
- Deviation from the mean = Difference between data and the mean
What is standard deviation?
The square root of the variance
What does the coefficient of variation (CV) measure?
The ratio of standard deviation to the mean, expressed as a percentage
- for interval or ratio data
What is a normal distribution?
A symmetrical, bell-shaped distribution with one mode
What is a bimodal distribution?
A symmetrical distribution with two modes
What is a rectangular distribution?
A symmetrical distribution where frequency is constant for all values
What is a positively skewed distribution?
A distribution where data points bunch up at the low end
What is a negatively skewed distribution?
A distribution where data points bunch up at the high end
What is the graphical representation for nominal data?
- Bar chart
- Pie chart
What graphical methods are used for ordinal data?
- Bar chart
- Pie chart
- Box-and-whisker plot
Which graphical methods are suitable for interval and ratio data?
- Box-and-whisker plot
- Histogram
- Line graph (time series)
- Error bar chart
What does an error bar chart depict?
Variability of data points, often representing standard deviation or confidence intervals
What does the measure of skewness indicate?
The degree of asymmetry in a distribution
What is the significance of a skewness value of 0?
Indicates a normal distribution
What does an absolute skewness value greater than 1 indicate?
Substantial skewness in the distribution
