descriptive stat hand

descriptive stat hand - Descriptive Statistics Central...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Descriptive Statistics Central Tendency Variability Shape PSY 2801: Summer 2010 Descriptive Statistics Jeff Jones University of Minnesota Jeff Jones Chs 4 and 5 Descriptive Statistics Central Tendency Variability Shape Descriptives versus Inferentials There are two major types of statistics that we will encounter in this course: 1 Descriptive Statistics e.g. mean, median, mode, range, variance, standard deviation, quartiles, midspread, skew, kurtosis, correlation The first 10 describe distributional properties of 1 variable The last 1 describes relational properties between 2 variables 2 Inferential Statistics e.g. z, t, χ 2 , F These try to get at how representative our sample is of a hypothesized population Jeff Jones Chs 4 and 5 Descriptive Statistics Central Tendency Variability Shape Descriptives versus Inferentials What do descriptive statistics . .. describe? Descriptive statistics can apply to both the sample and the population 1 Population: μ , σ 2 , ρ 2 Sample: ¯ x , s x , r xy Often, you will see a subscript “N”, indicating sample values e.g. ¯ x N This indicates that the average is only applied to the “N” people in the sample Furthermore, if a descriptive statistics will be used to test an inference, statisticians often put a hat over the parameter e.g. ˆ μ = ¯ x This indicates that ¯ x will be used to estimate the parameter value μ Jeff Jones Chs 4 and 5 Notes Notes Notes
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Descriptive Statistics Central Tendency Variability Shape Sum-things Important There are two mathematical things you should know: N X i = 1 blah i That math statement says “take the N observations of blah and sum them” blah could be anything: x i or ( x i - ¯ x ) 2 or 2 + 3 x i - x 2 i 4 x 3 i Just form the particular observation, make a table, and sum. Jeff Jones Chs 4 and 5 Descriptive Statistics Central Tendency Variability Shape Sum-things Important So let’s say we have observations: x = { 3 , 5 , 2 , 4 , 7 } and we want to find: N i = 1 ( x 2 i + x i + 2 ) Jeff Jones Chs 4 and 5 Descriptive Statistics Central Tendency Variability Shape Sum-things Important First: write down each piece of “blah” that you are trying to find x i x 2 i x 2 i + x i + 2 3 5 2 4 7 Jeff Jones Chs 4 and 5 Notes Notes Notes
Background image of page 2
Descriptive Statistics Central Tendency Variability Shape Sum-things Important Second: fill in the remaining pieces for each observation x i x 2 i x 2 i + x i + 2 3 9 14 5 25 32 2 4 8 4 16 22 7 49 58 Jeff Jones Chs 4 and 5 Descriptive Statistics Central Tendency Variability Shape Sum-things Important Third: sum down the column that contains “blah” for each observation x i x 2 i x 2 i + x i + 2 3 9 14 5 25 32 2 4 8 4 16 22 7 49 58 N X i = 1 blah i = N X i = 1 ( x 2 i + x i + 2 ) = 14 + 32 + 8 + 22 + 58 = 134 Jeff Jones Chs 4 and 5 Descriptive Statistics Central Tendency Variability Shape Rules of Summation Here are some rules of summation: 1 ( x i + y i ) = x i + y i 2 ( x i - y i ) = x i - y i 3 ( cx i ) = c x i 4 ( x i + c ) = x i + Nc 5 ( x i y i ) 6 = x i y i 6 x 2 i 6 = ( x i ) 2 7 ( x i + y i ) 2 = x 2 i + y 2 i + 2 ( x i y i ) Jeff Jones Chs 4 and 5
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 18

descriptive stat hand - Descriptive Statistics Central...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online