
IV Examples
 Mood when manipulated by researcher
 Movie when selected by researcher.

True IV:
QuasiIV:
Many quasiIVs are....
Researcher sets or manipulates IV
Researcher observes BUT DOES NOT MANIPULATE level
participant variables

QuasiIV
Researcher observes BUT DOES NOT MANIPULATE level

Example of QuasiIV
 Mood when participant shows up for study
 Movie when selected by participant
 Sex of participant

Cell or Condition
Ex:
A combination of IV levels
Study of sex differences among drivers in two countries (USA & Greece)

Confounding variable
Other names =
What do they do?
 AKA confound, covariate, or 3rd variable
 Affects DV. but is not an IV
 Can bias study, lead to wrong conclusion
 Ultimately has affect on IV
(IV STIMULUS > DV RESPONSE > Confounding variable > IV STIMULUS)


Whats the order
Date > ______ >
Data, statistical analysis, Information

What are the two types of statistics?
 Descriptive Statistics
 Inferential Statistics

Descriptive Statistics:
Goal?
Problems?
Best way to describe a variable is?
Summarize/Describe the data from your study (the sample)
Goal:Try to summarize data with two numbers without sacrificing crucial data:
 Average = Signal
 Variability = Noise
 Problems:
 Information loss
 Assumptions
Best way to describe a variable is by its type (nominal, ordinal, etc) and distribution

Inferential Statistics:
Are used to make predictions/inferences about the population based on the sample

Average:
Common averages:
Single value most typical of all data
 Mean =
 Meadian =
 Mode = Most freq value

Mode =
Works best for what distribution?
Used to describe?
Okay for what types of data?
 Most freq value
 Works best for unimodal distribution
 Used to describe average of nominal variable
 Okay for what types of data:
 (Ordinal Interval or Ratio)

Median =
APA format =?
 Apa = Mdn
 Divide Data in half ( 125 )

Mean =
Used to describe which data?

Mean = Best guess
average of interval or ratio variables, but only if distribution is unimodal and symmetric (not skewed)

IF distribution is unimodal and symmetric
Mode = Mdn = M

If distribution is unimodal with positive skew:
Mode < Mdn < M if unimodal

Would you report Mean, Median, or Mode?
Eye Color
Test Score (050) Normal Distribution
Test score (050) Highly Skewed Distribution
Temperature Normal Distribution
SIze of dog (small, medium, large)
Exam Grades (A, B, C, D, F)
INcome under (10k, 1020k, 2030 etc)
Eye ColorTest Score (050) Normal DistributionTest score (050) Highly Skewed DistributionTemperature Normal DistributionSIze of dog (small, medium, large)Exam Grades (A, B, C, D, F)INcome under (10k, 1020k, 2030 etc)

What is mean, median, mode of
1
1
4

Which would u use? Mean median mode
Small
Small
Small
Small
Medium
Medium
Medium
Large
Large
Mode????

Does average completely describe the data?
Solution?
No, because two distributions can have same average but look very different.
Need at least one other descriptive statistic.

Variation
Aka: Dispersion/Spread
*Single most typical difference from average
*Need to describe how much scores differ from average (ho wmuch noise is present)

IQR
Extends from?
Often used for?
Variabilities: How to measure them?
Range:
IQR:
 Interquartile Range Middle half of scores
 25th  75th percentile
 Ordinal Data
 Variabilities:
 Range = Largest datum  smallest datum
 IQR= Q3Q1
 where Q3 is the median of the upper half and Q1 is the median of the lower half of data. Q2 is the median of all data

Variance =
Squared Standard Deviation

Standard Deviation =
Know formula
Mean deviation from M, ignoring sign (sort of)

Standard Deviation
Different Mean =
Same Mean =
Different Mean =
 Different Mean = Same SD
 Same Mean = Different SD
 Different Mean = Different SD

Descriptive Statistics to report in Method Section/Participant subsection
 Sex: # of M & # of F
 Age: Min, Max, and either M and SD (of symmetric) or Mdn and IQR range (of skewed)
Other key demographics such as ethnicity if important

Descriptive Statistics of DV to report in...
 Results Section
 If DV is nominal or ordinal with few levels:
 Mode for each cell
 If DV is ordinal, or interval/ratio and skewed: n, Mdn, and IQR rang for each cell
If DV is interval/ratio and symmetric: n, M, and SD for each cell

Descriptives calculate:
M, SD, Min, and Max

