Lecture 4 - Central Tendency and Variability Flashcards
What are the desirable properties of an operation (for example, a measure)?
the desirable properties of an operation are validity (how well the states of the variable reflect the states of the construct) and reliability (insensitivity of the variable to states of other constructs, roughly the consistency of the variable’s states when they should be consistent)
provide an example of evidence that suggests a measure has low reliability
participants take the same extraversion questionnaire twice with a one-week gap in between. The results show that many of the highest-scoring participants in week one are among the lowest-scoring in week two
how can variation in nominal variables be described using numbers?
Variation in nominal variables can be described using counts of each state and relative frequencies (percentages). For example, if tree types are counted, the counts of each tree type and their relative frequencies are used.
what are some descriptive numbers used for interval/ratio variables?
descriptive numbers for interval/ratio variables include counts of each state, relative frequency (%), cumulative frequency, percentiles and counts or percentages within a range
what are the three measures of central tendency?
the three measures of central tendency are the mode (the most common score), the median (the score that 50% of scores fall below), and the mean (the sum of scores divided by the number of scores)
what are the qualities of the mode as a measure of central tendency?
the mode is easy to understand, meaningful with nominal data, but is unaffected by the presence and size of other scores, and does not fully represent the whole distribution
what is the simplest way to describe the spread of scores, and what are its qualities?
the simplest way to describe the spread is the range, which is the difference between the highest and lowest score, it is easy to understand but unaffected by most scores.
explain why total deviation from the mean sums to zero and how this issue is addressed.
Total deviation from the mean sums to zero because positive and negative deviations cancel each other out. This issue is addressed by using squared deviation to calculate variance
how is variance calculated, and what are its qualities?
variance is calculated by summing the squared deviations from the mean and dividing by the number of scores. It represents the deviation of all scores around the mean but is hard to understand as it is the mean squared deviation.
How is the standard deviation derived from variance, and what are its qualities?
the standard deviation is derived by taking the square root of the variance. It represents the deviation of all scores around the mean and is easier to understand as it roughly indicates the average deviation
