PSYC 2260 Lecture Notes - Lecture 2: Standard Deviation, Central Tendency, Squared Deviations From The Mean

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26 Jun 2018

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PSYC 2260 Introduction to Research Methods in Psychology

Chapter 2 Central Tendency and Variability

2 Type of descriptive Statistic:

1.Central Tendency

Measures of central tendency

- The mean (the arithmetic average): average of data

- The mode: the most frequency occurring score in a set of data

- The median: the middle score in a range of scores (the 50t percentile)

*in perfectly bell-shape distribution, the mean = the mode = the median

Sometimes the median can be more representatives than the mean

Outlier: score with an extreme value in relation to the other scores in the distribution

2.Dispersion

Measures of dispersion

Range (2 types)

1. Potential range: distance between lowest & highest possible score

2. Obtained range: distance between lowest & highest actual score

Variance and Deviation

1. Variance SD2

-Definitional formula: the average of the squared deviations of the scores from the mean

SD2 = sum of (X-M)2 / N

Directly showing the meaning of the procedure

-Computational formula (short cut):

Does not directly show the meaning of the procedure

- Use N-1 when researcher have score from a particular group of people and researcher want

to estimate what the variance would be for the larger group of people whom these

individual represent

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