2Measures of Central Tendency Mode: The most frequently occurring score in a distribution.Mean: The arithmetic average of scores in a distribution obtained by adding the scores and then dividing by the number of scores that were added together.Median: The middle score in a rank-ordered distribution.OBJECTIVE 17| Describe three measures of central tendency and tell which is most affected by extreme scores.
3M&Ms Activity Quantify (count) the data within the bag=total M&Ms 2) Classify candy by color and count each color-list each color total on your work paper
4M&M Activity 3) Determine the groups quantity (total) 4) Calculate the groups mean* Work with your own pieces now5) Calculate the mean6) Calculate the mode7) Calculate the medianBi-modal=> two categories with the same mode
5Measures of Central Tendency A Skewed Distribution
6Measures of VariationRange: The difference between the highest and lowest scores in a distribution.Standard Deviation: A computed measure of how much scores vary around the mean.OBJECTIVE 18| Explain two measures of variation.
7M&M Activity Find the range of group’s bag quantity *Highest # of m&ms-lowest # of m&ms8) Find the range of colors in individual bag9) Calculate Standard Deviation-a measure of spread
8Standard Deviation Determine the mean Subtract the mean from every number to get the list of deviations (negative numbers are ok)Square the resulting list of numbersAdd up all the resulting squares to get their total sumDivide your result by one less than the number of items in the listTo get the SD, take the square root of the resulting number
9Practice Standard Deviation your list of numbers: 1, 3, 4, 6, 9, 191) mean: ( ) / 6 = 42 / 6 = 72) list of deviations: -6, -4, -3, -1, 2, 123) squares of deviations: 36, 16, 9, 1, 4, 1444) sum of deviations: = 2105) divided by one less than the number of items in the list: 210 / 5 = 426) square root of this number: square root (42) = about 6.48
11Making InferencesA statistical statement of how frequently an obtained result occurred by experimental manipulation or by chance.
12When is an Observed Difference Reliable? Making InferencesWhen is an Observed Difference Reliable?Representative samples are better than biased samples.Less variable observations are more reliable than more variable ones.More cases are better than fewer cases.OBJECTIVE 19| Identify three principles for making generalizations from samples.
13When is a Difference Significant? Making InferencesWhen is a Difference Significant?When sample averages are reliable and the difference between them is relatively large, we say the difference has statistical significance (how likely it is that an obtained result occurred by chance)For psychologists this difference is measured through alpha level set at 5 percent (.05)OBJECTIVE 20| Explain how psychologists decide whether differences are meaningful.