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Psychology 3800F/G Final: 3800F/G - Final Exam Notes, pt. 1

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Psychology 3800F/G
Ryan Stevenson

Scales properties of measurement vars defined in terms of 4 categories; have implications Nominal: identity; ordinal: rank order; interval: equal unit size; ratio: absolute zero Pops: large set of s; finite, infinite, theoretical pops; 3 types: o Finite: definite of indls o Infinite: no limit on of indls (no upper limit) o Theoretical: an equation; e.g., a norm pop Under approp circumstances, can estimate frequency of each value in pop Statl inference based on theoretical pop Model underlying tests of signif assumes pop is norm Samples: subset of a pop o RS: every obs in pop has equal chance of being selected not representative obt a stratified RS Identify params of pop RSs from strata o NonRS: equal chance is not the case o Inferential stats (tests of signif) all based on assumption of random sampling Concerned with estimating prob a certain value would be obt if RSs from norm pop with given characteristics (assumption of normality) o If pop not norm, need all other conditions satisfied Results conform to ones obt from random sampling from norm pops Stat: describing sample (mean, std. dev., variance) Param: describing pop (mu, sigma, sigma ) 2 o Stats vary from sample to sample, even when param is constant Unbiased estimate: mean of all possible values of that stat = to param o Why: mean of the means of all possible samples = pop mean Biased estimate: mean of all possible sample values (stats) == to pop value (param) o Why: variance is biased bc mean of variances of all samples < pop variance Types of Descriptive Stats Params (4) 1) Stats of Location locate the sample or pop on the line (in space) (infinity to +infinity) Measures of central tendency (averages): minimize distance btwn central value all data points o Median: value at center of all values (50 above below); 50 percentile Distance: defined by magnitude o Mode: value that occurs most frequently Distance: defined as a binary < or > Bimodal: 2 same high frequency values (2 modes) Multimodal: > 2 modes o Mean: sum of devs of scores from their mean add to 0 Distance: defined as a hit or miss xbar = (sum of values) ( of values) Lowest highest thlue in the sample th Percentiles 25 percentile: 25 of values are lower 75 are higher; 75 percentile: opposite Deciles, quartiles, etc. 2) Stats of Scale Describes how much differentiationvariability there is in the sample; A.k.a., stats of variation or dispersion o Small scale: s close together o Large scale: values spread out cover wide range on line Range: diff btwn highest lowest values o Simplest measure of scale; useful in a relative sense (comparisons) o Problem: based on only 2 values; range will vary in each sample o Desirable to have all measures in defn of stat; more stable from sampling POV Semiinterquartile range (quartile dev): [(diff btwn 75 25 ) 2]th o Uses more info in distrib; based on more values in sample; more stable than range
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