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PSYB01H3 (581)
Chapter 10

Chapter 10

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Department
Psychology
Course
PSYB01H3
Professor
David Nussbaum
Semester
Fall

Description
Chapter 10- Quantitative Data Analysis Does Spending Money on Others Promote Happiness Statistical Approach o Descriptive Statistics: describe variables in a study; one at a time and in relation to another o Inferential statistics: used to estimate characteristics of a population from those found in a random sample of the population; can be used to test hypotheses about the relationship between variables; likelihood of results due to chance Levels of Measurement Matters o Nominal, ordinal, interval, ratio: determines which ties of statistic analyses you can use (see chapter 4) Univariate Distributions o Univariate distribution: a probability or frequency distribution of only one variable Frequency Distributions: shows the number of cases and/or % of cases who receive each possible score on a variable o Many require grouping of some values so it can fit on a table and so distribution will be clearer and more meaningful o Categories should be logically defensible and preserve distribution shape and should be mutually exclusive and exhaustive o Preferable to graphing when exact number of cases has to be stated or when lots of distributions have to be shown in compact form Graphing: to depict frequency distributions o Bar chart: solid bars separated by spaces; good for nominal level o Histogram: shows frequency distribution of a quantitative variable Beware of Deceptive Graphs o Guidelines  Begin graph of quantitative variables at 0 on both axes; can break this rule at times ex. Age distribution of adults; should show break clearly  Always use bars of equal width  Two axes should be of approximately equal length  Done have chart 'junk' that can obscure distribution shape Descriptive Statistics o Important features of shape: central tendency, variability, and skewness o Statistic for skewness is only appropriate for quantitative variables but is rarely used and isnt discussed Measures of Central Tendency o To choose which consider level of measurement, skewness of distribution and purpose of statistic o Mode/probability average: most frequent value; used least often as it can be misleading  Bimodal vs unimodal  Might fall far from main cluster of cases in distribution o Median: position average; cant be done in nominal  In frequency distribution determine it by identifying the value corresponding to a cumulative % of 50 o Mean: arithmetic average; sum of value of all cases/# of cases; only in interval or ratio or if ordinal treat as an interval? o Median vs. Mean  Mean is technically inappropriate for ordinal but in practice is used  If symmetric use either, if skewed use median  Most important consideration is purpose of statistical summary  Neither is appropriate at nominal level Measures of Variation o Must be at interval or ratio level although some argue they can be used with ordinal-level measures o Range: highest value-lowest value +1; not great as can be affected by outliers o Varianc2: average2squared deviation of each case from the mean  σ = Σ(yi- i) /N o Standard deviation: square root of the variance; when calculated from sample data denominator is supposed to be N-1 not N (no effect when N is large)  Can show how much variation, dispersion, or spread there is in a set of scores, numbers or data points and how far from the average a particular score is Sampling Distributions o Value of mean or any other statistic from random sample is not likely equal to population parameter o Sampling distribution: distribution of the means of all the possible samples from the population; mean is population mean o Standard error to the mean: statistic that indicated the degree to which the means of the samples vary from the population mean; estimate of stdev of sampling distribution Inferential Statistics o Confidence limits: assume normal distribution; probability that sample statistic falls in certain range of population parameter  Normal distribution: from chance variation around the mean  -1stdev<65%
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