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# Week 3 Notes - Psychology 211 Psychology 211

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## Popular in Psychology 211-003 Elem Statistical Methods

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This 6 page Class Notes was uploaded by Kennedy Patterson on Sunday February 8, 2015. The Class Notes belongs to Psychology 211 at University of Alabama - Tuscaloosa taught by Andre Souza in Spring2015. Since its upload, it has received 131 views. For similar materials see Psychology 211-003 Elem Statistical Methods in Psychlogy at University of Alabama - Tuscaloosa.

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Date Created: 02/08/15

Chapter 4 1161512115 an object with rows and columns different observations contain the values of different variables US What affects student s grades i Age H Gender iii Relationship status iv Hours spent on Facebook v Number of friends on Facebook vi Drinking habits a 6 columns b X amount of rows c Cannot have more than 1 column to represent data Male Female Wrong lID Yes No 3 a Everything varies yet measurements often cluster around certain values b Shows what the t ical observation is 4 Sample Statistic I Sample Statistics are not the same everything varies amp varies around Sample Statistic 2 2 central number X y etc always lower case X age y relationship status individual values i X1 X2 X3 c Individual values of the variable are represented by subscript i lnX 23 32 45 65 77 ii X1 23 X2 32 X5 77 d To refer to a single score without saying which one it is we use Xi e Sometimes subscripts may be omitted g OOIO Chapter 4 f 1161512115 i Z sum of everything that follows ii 2X sum of all the X s 1 Example if there are 30 values for X a X1 12 X2 45 X3 44Xn 21 we say n 30 N 2X sum of all X s from i1 to in 1 202 is different than 28 i X 1112 X y XV 2X 5 1 20 20 z 2 25 1 19 19 220 12121222 7 1 19 19 X 2 19 38 ArithmeticMean a b X bar I the mean is the sum of all the data points ZX divided by the number of data points n Mathematically i A a ZXn n 1112 i 54 Answers the question if all the data points had the same value what would the value be If I want all the data points to be the same and still have the same sum what would this number be What ifI asked these people to give me all the money they have Ca os250 Kevin 153 Stephanie 76 Mary 198 Total 677 I ZXn 9 6774 16925 Mean 16925 16925 X 4 677 Chapter 4 1161512115 g h i J C m 321 222 n 3 ZX 6 na zx 32 3 Mean 1 2 9 number to replace every data set to keep same total 9 a Mean equals the proportion observations that equal 1 b asked 9 women how many men they have dated in the past 12 months Boyfriend 0 O I ZXn 49 1 1 is recorded 4 times 1 9 is the total number 0 O 1 1 9 O c Arithmetic mean is the only single number for which the defined as the difference each data point amp the mean sum to zero X 3 21 iL 1 21 14oo 12 220 2 2 i2 Residual O Chapter 1161512115 1 middle score in an ordered set or data a b The score corresponding to the point having 50 of the observations below it when the observations are arranged in numerical order the location of the median in an ordered series 2 a b 32 34 35 35 36 38 38 42 42 42 44 44 100 i Middle value 38 ii 13 12 7th number 9 median 38 c F i 12 12 65 9 between 6 amp 7 1 Average of number median 9 avg of 38 amp 38 38 3 a The median like the arithmetic mean is appropriate for b Since it requires ordered data the median is also appropriate for c The median is which makes it an appropriate measure for skewed distributions d The median is not very informative for discrete data that takes only a few values e The US Census asked how many relationships have you had in the last 12 months i Only 6 distinct responses occurred O12345 and 638 of them was 1 ii The median is 1 because more than 50 of the total was 1 4 l the sum of the scores divided by the number of scores avera e 5 mean after discarding fixed percentage of extreme observations a take one or more of the largest and smallest values in the sample set them aside and take the mean of what remains b For a 10 trimmed mean we would set aside the largest 10 of the observations and the lowest 10 of the observations the mean of what remained would be the 10 trimmed mean 6 a For processes that change multiplicatively rather than additively arithmetic mean is not a good measure b Th xk n Chapter 4 1161512115 Also indicates the central tendency but uses the product x instead of Ex x x x 30 9 x i Multiili the same numbers to get same product record the cumulative amounts of tweets written in last 6 months Month Number of Tweets Increase Rate July 132 August 158 1997 September 169 697 October 188 1124 November 221 1755 December 240 86 i How to find increase rate Take the first value subtract from the second value and divide by the first value 1 158132 1997 132 Percentage not independent of each other Increase rate depends on previous month nnx x 511997 x 697 x 1124 x 1755 x 86 1187 1187 Geometric Mean Arithmetic means are good for independent events scores on a test Geometric Means are good for the numbers that are not independent of each other percentages i n x ZXi The same loiic aiilies to the claeometric mean i Axn x Chapter 4 1161512115 7 the most common value highest region of distribution a Commonly used with highly discrete variables such as categorical variables through it is appropriate for all types of data b F c number of girls dated in the past 12 months i Mode quot2quot amp Mexico 1 2 is in the chart 3 times 2 Mexico has the most number of girls Nationalitv Number of Girls Brazil 3 Russia India Mexico Peru Cmumbm United States Canada NLNmVNI t

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