Welcome to MM570 Applies Statistics for Psychology Unit 2 Seminar Dr. Bob Lockwood.

Welcome to MM570Welcome to MM570Applies Statistics for Applies Statistics for

PsychologyPsychology

Welcome to MM570Welcome to MM570Applies Statistics for Applies Statistics for

PsychologyPsychologyUnit 2 Seminar

Dr. Bob Lockwood

Measures of Central Tendency: The Mean

Measures of Central Tendency: The Mean

• Sum of all the scores divided by the number of scores

• Mean of 7,8,8,7,3,1,6,9,3,8• ΣX = 7+8+8+7+3+1+6+9+3+8 = 60• N = 10• Mean = 60/10 = 6

The MeanThe Mean

Mean of the distribution of the number of dreams during a week for 10 students.

Measures of Central Tendency: The Mode

Measures of Central Tendency: The Mode

• Most common single number in a distribution

• Mode of 7,8,8,7,3,1,6,9,3,8 = 8

• Measure of central tendency for nominal

variables

The ModeThe Mode

The mode as the high point in a distribution’s histogram, using the example of the number of

dreams during a week for 10 students.

Measures of Central Tendency: The Median

Measures of Central Tendency: The Median

• The middle score when all scores are arranged from lowest to highest

• Median of 7,8,8,7,3,1,6,9,3,8

• 1 3 3 6 7 7 8 8 8 9

median

• Median is the average (mean) of the 5th and 6th scores, so the median is 7

Measures of Central Tendency Types of Data

Measures of Central Tendency Types of Data

Measure of Central Tendency Type of Data Mode Median Mean Nominal Yes No No Ordinal Yes Yes No Equal Interval* Yes Yes Yes Ratio* Yes Yes Yes

SPSS refers to these as Scale data. The reason is based on this table, in terms of

statistical analyses; there is no difference between equal interval and ratio data.

Measures of Variability:The Variance


• The average of each score’s squared difference from the mean

• Steps for computing the variance:1. Subtract the mean from each score2. Square each of these deviation scores3. Add up the squared deviation scores4. Divide the sum of squared deviations by the number of scores



• Formula for the variance:

Measures of Variability:The Standard DeviationMeasures of Variability:The Standard Deviation

• Most common way of describing the spread of a group of scores

• Steps for computing the standard deviation:1. Figure the variance2. Take the square root

[Hint: I use SPSS]

Measures of Variability:The Standard DeviationMeasures of Variability:The Standard Deviation

• Formula for the standard deviation:

Table 2-4: Figuring the Variance and Standard Deviation for Number of Social Interactions during a week for 94 College Students (page 48)

Table 2-4: Figuring the Variance and Standard Deviation for Number of Social Interactions during a week for 94 College Students (page 48)

Number of Interactions - Mean number of Interactions

= Deviation Score

Squared Deviation Score

48 - 17.39 = 30.16 936.9715 - 17.39 = -2.39 5.7133 - 17.39 = 15.61 243.67-- -- 35 - 17.39 = 17.61 310.119 - 17.39 = -8.39 70.39

30 - 17.39 = 12.61 159.018 - 17.39 = -9.39 88.17

26 - 17.39 = 8.61 74.13 ∑: 0.00 ∑: 12,406.44

Controversies and Limitations:The Tyranny of the Mean

Controversies and Limitations:The Tyranny of the Mean

• Knowledge about the individual case is lost when taking averages

• Qualitative research methods• e.g., case studies, ethnography

Using SPSS Mean, Median, Mode, Variance and Standard DeviationUsing SPSS Mean, Median, Mode, Variance and Standard Deviation

Enter the scores in one column of the Data Window Analyze Descriptive Statistics Frequencies the variable you want to make a frequency table of the arrow, then Statistics Mean, Median, Mode, Variance, Standard Deviation Continue OK

SPSS Numerical Descriptors 1SPSS Numerical Descriptors 1

SPSS Descriptive Statistics – Descriptives

SPSS Descriptive Statistics – Descriptives

QUESTIONS??QUESTIONS??

Welcome to MM570 Applies Statistics for Psychology Unit 2 Seminar Dr. Bob Lockwood.

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