Exam 2 Flashcards
Scales of Measurement
Nominal, Ordinal, Interval, and Ratio Scales
- Importance: the different scales allow data to be analyzed and processed in different ways
Nominal Scale
Classification/categorization of objects/individuals
- Order doesn’t matter
- No numerical meaning
Examples
- male vs. female
- ethnicity
- favorite color
Ordinal Scale
Classification/categorization of objects/individuals where the order of categories has meaning
- Unequal differences between categories, intervals aren’t necessarily the same
Examples
- Placement in a race
- Ranking favorite ice cream flavors
- Grades
Interval Scale
Categorization of something where order matters and scales of measurement are equal
- Don’t have true zero value
- True zero value: when zero means the nonexistence of the measure (such as 0 people in a population would be an absence of people)
Examples
-Temperature
Ratio Scale
Categorization of something where order matters and scales of measurement are equal, and where there is a true zero
- The ratios are meaningful (eg. x is 3x as much as y)
Examples
- Height
- Age
- Weight
Measures of Central Tendency (Averages)
Mode (bimodal and multimodal), median, mean, and outliers
Mode
The score that occurs most often
- Can be used with any scale
- Only average that can be used for nominal scale data
Bimodal: two scores occur equally often + most frequently
Multimodal: three + scores occur equally often + most frequently
Median
The middle point in a set of scores
- 50% of scores fall above this point, 50% below this point
- Can be used for ordinal, interval, and ratio scales
Mean
The arithmetic average found by adding all scores and dividing by the number of scores
- Can be used for interval and ratio scales
- May be biased by outliers
Outlier
Extreme values much higher/lower than the majority of scores
- Greatest effect on mean
- Wont largely impact median and mode
Measures of Dispersion
How spread out data are
- Includes range (inclusive and exclusive), standard deviation, and variance
Range
Distance from highest to lowest value
Inclusive: Highest score - lowest score + 1
Exclusive: Highest score - lowest score - 1
- Outliers ruin
Standard Deviation
Expresses average distance of scores from the mean
- Only calculated on interval/ratio data
Variance
Standard deviation squared
- Only calculated on interval/ratio data (requires mean)
Correlation
The degree of a relationship between 2 variables
- Range between -1.00 - 1.00
- Correlation does NOT mean causation
Strength
- absolute value of correlation
- - .90 > .70, .90 > .70
Direction
- positive: when one variable increases, other also increases (and vice versa)
- negative: when one variable decreases, the other increases (and vice versa)
Bivariate Correlation Coefficient
Correlation coefficient is referred to as this when the relationship between two variables is being assessed
Types of Correlation
Pearson’s product-moment correlation (Pearson’s r)
- used with interval/ratio data
Spearman’s rho (p)
- if one or both variables are ordinal
Multiple Correlation
Correlation between multiple variables and one particular variable
- Single score
- 0.00 - 1.00
Multiple regression
- similar but gives info about each predictor variable (individual contributions)
Limits of Correlations
-There a different kinds of correlations for different kinds of data
- It is only evidence of a relationship not a cause
Error Variance
Natural fluctuations in group caused by something other than independent variable
- Differences within a group
- one measure = standard deviation
- Can be used to find significant difference by completing the equation: differences between groups/differences within groups = effect of independent variable + error variance/error variance
T-Test
Used to compare two groups to determine if there is a significant difference between them
Analysis of Variance (ANOVA)
Used to compare three+ groups to determine if there is any significant difference
Between-Groups Variance
Measurements found by testing different groups on different variables
Pros: Prevents carryover effect
- Shorter duration
- Reduces impact of variables
- Results are easier to interpret
Cons: Requires more participants
- Individual differences can cause results
Within-Groups Variance
Measurements found by testing the same group/individual on different variables
Pros: increased statistical power
- Control for individual differences
- Potential reduced error-variance
Cons: Possibility for order effects
- Carryover effects
- Practice effects
- Time measurement effects
Parameter
Characteristic of a population
Parametric tests
Makes assumptions about population characteristics
- Only usable with interval/ratio data
Nonparametric tests
Makes no assumptions about population characteristics