Here it is….Here it is….

…Your Super Duper…Your Super DuperFaster than EverFaster than EverPooper Scooper Pooper Scooper Review of Statistics Review of Statistics and Data Analysis!and Data Analysis!

Types of DataTypes of Data

NominalNominal – identifies categories – identifies categories e.g. gender, color, yes/noe.g. gender, color, yes/no

OrdinalOrdinal – identifies rank order – identifies rank order e.g. class ranke.g. class rank

IntervalInterval – falls in a number line with an – falls in a number line with an absolute zero (which means “the absence of”)absolute zero (which means “the absence of”) e.g. height and weighte.g. height and weight

RatioRatio – falls in a number line, but 0 is just – falls in a number line, but 0 is just another number another number e.g. temperaturee.g. temperature

Figure 1.10 A skewed distributionMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

Descriptive StatisticsDescriptive Statistics

Measures of Central TendencyMeasures of Central Tendency mean, median, mode (Which is easily skewed?)mean, median, mode (Which is easily skewed?) If the 3 are =, you have bell curve. If not, a skew.If the 3 are =, you have bell curve. If not, a skew.

Positive skew = scores pull mean higherPositive skew = scores pull mean higher Negative skew = scores pull mean lowerNegative skew = scores pull mean lower Question: Which skew is this an example of?Question: Which skew is this an example of?

Measures of VariationMeasures of Variation Range (crude estimate)Range (crude estimate) Standard Deviation – the higher the Standard Deviation – the higher the

number, the greater variability of scoresnumber, the greater variability of scores

Table 1.4 Source: Myers, Psychology, Eighth Edition, Copyright © 2007 by Worth Publishers

Inferential StatisticsInferential Statistics In order to generalize from samples…:In order to generalize from samples…:

Use representative samplesUse representative samples Use larger sample sizesUse larger sample sizes Observations with low variability are more reliableObservations with low variability are more reliable

Statistical SignificanceStatistical Significance – the likelihood that – the likelihood that the difference in samples’ means is due to the difference in samples’ means is due to chancechance Goal is a significance of .05 or less Goal is a significance of .05 or less In other words, it is only 5% likely the difference is In other words, it is only 5% likely the difference is

due to chance (or 95% likely the difference may be due to chance (or 95% likely the difference may be attributed to the Independent Variable)attributed to the Independent Variable)

Figure 1.3 Scatterplots, showing patterns of correlationMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

CorrelationCorrelationCorrelation Coefficient – a statistical measure of the strength of the relationship between variables

e.g. -.37 (number indicates strength, sign indicates direction of correlation)

Ranges from -1.00 to +1.00

Positive Correlation – two factors increase or decrease together (“DIRECT” correlation)

Negative Correlation – one factor increases as the other decreases (“INVERSE” correlation)

Figure 1.5 Three possible cause-effect relationshipsMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

Correlation does NOT equal Correlation does NOT equal Causation!Causation!

People with low self-esteem are more People with low self-esteem are more likely to report depression. Why?likely to report depression. Why?

Experimental DesignExperimental Design

Between-subjects design:Between-subjects design: Compares one group of people to anotherCompares one group of people to another Most common methodMost common method Efficient method, but individual differences of the Efficient method, but individual differences of the

people may influence the resultspeople may influence the results Within-subjects design:Within-subjects design:

Compares participants to themselvesCompares participants to themselves Pre-test Pre-test Ind. Variable Ind. Variable Post-test Post-test Less efficient and more time-consuming, but Less efficient and more time-consuming, but

resistant to the possible effects of individual resistant to the possible effects of individual differencesdifferences

For More Practice…For More Practice…

Use the PsychSim Tutorials on the Use the PsychSim Tutorials on the textbook websitetextbook website!!

Click on “PsychSim Tutorials” and then Click on “PsychSim Tutorials” and then Click on Chapter 1, “Descriptive Click on Chapter 1, “Descriptive Statistics” and/or “Correlation Analysis”Statistics” and/or “Correlation Analysis”