W1 Chapter 3A - Essentials Statistical Concepts Flashcards
How can large amounts of data collected in tests be used in a meaningful manner?
By summarising data using statistical tools like measures of central tendency
One way of summarising data is to tabulate a frequency distribution. What is frequency distribution?
A tally of how many scores of a specific equal-sized class interval fall into each interval
What range of class intervals is common for frequency distributions?
Between 5 - 15 class intervals
What other type of graphical representation contains the same information as frequency distributions?
Histograms
What component of a histogram represents the number of scores within that class interval?
The height of the column
How does a frequency polygon differ from a histogram?
The frequency of class intervals is represented by a single point rather than a column, and the points are connected with a line
What are the 3 type of measure of central tendency?
- Mean (average)
- Median (Middle)
- Mode (most frequent)
What can make the mean unreliable?
A few extreme high or low scores
When is the median a better measure of central tendency?
When the distribution of score is skewed, or asymmetrical.
What is the most commonly used statistical index of variability in a group of scores?
Standard deviation
What does the standard deviation represent?
The degree of dispersion in a group of scores
What 2 statistical indices is used to describe the degree of dispersion in a distribution?
- Variance
- Standard Deviation
What is the relationship between variance and standard deviation?
The standard deviation the the square root of the variance
What is the preferred measure of variance?
Standard deviation
How is a normal distribution defined?
By a symmetrical, mathematically defined bell curve
What are the 3 reasons why a normal distribution is preferred?
- A normal distribution has useful mathematical features that form the basis for several kinds of statistical investigations (such as the t-test)
- Mathematical precision
- A normal curve often arises spontaneously in nature
What is the percentage of cases within one standard deviation?
68.26%
What is the percentage of cases within two standard deviations?
95.44%
What is the percentage of cases within three standard deviations?
99.72%
What does skewness refer to?
The symmetry or asymmetry of a frequency distribution
What is positive skewness?
When the test scores are piled up at the low end of the scale
What is negative skewness?
When the test scores are piled up at the high end of the scale
What can be done when an instrument produces sewed results?
A statistical transformation can be used to produce a more normal distribution
