Stats 6
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What is the mode?
The most commonly occurring value in the data set

What is the median?
 A value that divides the sample scores into two halves
 Equal numbers of scores lie above and below the median

How might one find the median for a data set?
 For an odd number of figures, take the middle value
 For an even number, take the middle two, add them and then divide the total by 2

How might one calculate the arithmetic mean?
Find the sum of all values and divide that figure by the number of values

What do Y values represent?
The scores for data sets

What does Y (bar) represent?
The mean of values in the data set

What does ∑ represent?
 The operation of addition
 (∑Y: add up all Y values)

How can the mean be said to be a balance point?
The sum of distances before the mean is equal to the sum of distances after it

If the variable is categorical, what is the most appropriate measure of central tendency?
The mode

If the distribution is normal (symmetrical with no outliers) what is the most appropriate measure of central tendency?
The mean

What effects does a positive skew have on measures of central tendency?
 The mode stays the same
 The median score increases (higher than the mode)
 The mean score increases (higher than the median)

What effects does a negative skew have on measures of central tendency?
 The mode stays the same (for the distribution of scores)
 The median score decreases (lower than the mode)
 The mean score decreases (lower than the median)

What are the relevant sensitivities of the mean?
 Sensitive to the exact values of all scores in the distribution
 Very sensitive to extreme scores (outliers)
 More sensitive than the median to outliers or legitimate data points that lie on the fringes

What are quartiles?
Divisions of data into quarters

What are the tree quartiles?
 Lower quartile: Divides the first 25% of the scores from the upper 75%
 Median: Divides the first 50% from the second half
 Upper quartile: Divides the fist 75% from the upper 25%

What is the range?
 The difference between the highest and lowest scores
 It is only based on two scores, however and is unstable and vulnerable to outliers

What is the interquartile range?
 The difference of the values of the third and first quartile
 Q3Q1
 Sometimes called the midrange as it it the range of the middle 50% of scores

What are the deviation scores?
The value of the Y scores minus the mean

What is the mean of deviation scores?
 0
 This is because the scores always sum to 0

What are absolute deviations?
 The removal of minus signs from the deviation scores
 This is valid, but is rarely used

What is the variance?
 The degree of dispersion of results around the mean
 Each score is represented as a deviation and dispersion is measured in terms of the size of deviation

What is the sum of squares?
 The sum of the squared mean values
 SS= ∑[YY(bar)](squared)

What is the variance?
 The sum of squares divided by the number of results 1
 n1 is known as the degrees of freedom

What is the standard deviation in relation to variance?
The square root of the variance value

Why is the standard deviation better than the variance?
It is in the same units of measurements as the original score

What us the symbol for variance?
s(squared)

What is the symbol for standard deviation?
s