Descriptive Statistics

Question 1

What is a measure of central tendency?

Answer 1

One score that summarizes the data.

The most representative score of a set of observations.

Question 2

Three common measures of central tendency

Answer 2

Mean - average of a set of #s
Median - # dividing the distribution in half
Mode - most frequent score in a distribution

Question 3

What is the preferred measure of central tendency and why?

Answer 3

Mean, it uses all the information available.

Question 4

Three situations in which you might use other measures of central tendency other than the mean?

Answer 4

Skewed data (outliers affect the mean)
Nominal or ordinal data (you would use the mode)
- one more?

Question 5

Components of a frequency distribution table

Answer 5

Column 1 - X - categories of scales of measurement
Column 2 - F - frequency of each score
Column 3 - F(x)
Column 4 - F(x)^2

Question 6

Calculations from frequency distribution table

Answer 6

N = F/sum(F)
Sum(F) = SumF(x)
M = Sum(F)/N

Question 7

Four rules of making a grouped frequency distribution table

Answer 7

1. Should have 10 intervals.
2. Width of intervals is simple.
3. Bottom score should be a multiple of the width.
4. All intervals should be the same width.

Question 8

Variability

Answer 8

Dispersion of scores

Quantitative measure of degree to which scores in a distribution are spread out or clustered together

Question 9

What is range and what is it’s primary limitation?

Answer 9

Highest score to lowest score

Only based on two scores in the entire distribution.

Question 10

Standard deviation

Answer 10

the average deviation between individual scores in a distribution.
Tells you how spread out the scores are.

Question 11

Steps to calculate standard deviation

Answer 11

Deviance scores - each score minus the mean
Squared deviance scores - squaring the deviance scores
Sum of squared deviance
SS/df = variance
Square root of variance = standard deviation

Question 12

Three things that help determine meaningfulness of data

Answer 12

Statistical significance (p-value)
Practical significance (effect sizes)
Confifence Intervals

Question 13

Three types of random influences

Answer 13

Random generation
Random sampling
Measurement error

Question 14

Why use descriptives?

Answer 14

Simplified, easy to get to main point, systematic, basis for inferential stats

Question 15

Types of kurtosis

Answer 15

lepto (higher)
meso (normal)
platy (lower)