Week 2 Flashcards
Data Types - Nominal Data
- Uses numbers as labels
- Denotes group membership
- Can be called Categorical Data
- Does not reflect magnitude or order in any way
E.g. gender: 1 = woman, 2 = man, 3 = non-binary, 4 = another gender
Nominal date
- Common in psychological research
- Often used in experimental design
- Can be presented as frequency or percentage
Data Types Ordinal Data
- Also called Rank Data
- Used to rank order, so has magnitude
- Does not tell us how different the rankings are
e.g. positions in a race 1st, 2nd, 3rd but not individual times - cannot use ordinal data to make inferences
Data Types - Interval Data
- Also called Continuous Data
- Does not have a real Zero Point
- No way of assessing absence of a construct this way
e.g. Although Celcius temperature has a zero value it can continue beyond into negative figures. Temperature gets colder, it does not dissappear
Zero Point
- Point on a scale that denotes zero
- From here, positive and negative readings can be made
- The point from which progress can be charted.
Data Types - Ratio Data
- Also called continuous Data
- has a highest level of measurement
- Similar to interval data equal in scale
But in addition to order intervals might be different i.e. times in a race - Has equal magnitude and an Absolute Zero
e.g. weight data, bunch of apples equals a kilo, as we remove apples weight goes down but when last apple is removed we get zero
Types of Data
- Nominal Data
- Ordinal Data
- Interval Data
- Ratio Data
Different statistical tests such as test of Correlation has miminum requirement for Interval Data.
Many psychological measures area hybrid of Interval and Ratio Data
Correlation
- Correlation is key when looking at measurement
- Basis for reliability, validity, factor analysis
- Allows for assessment of individuals
- Individual variations are important factors of biological and social beings
Correlational Psychologists
- their goal is to predict variation within a treatement
- demand uniform treatment for each case
Explain Within Groups Variability
- Look for an association with the within groups variability of another variable
- Scatter Plot charts with x & y axis can measure two variables
e.g. marks on a test within the group of a classroom
Quantify Relationships Between Variables
- Measures magnititude (strength) and direction (Positive or negative)
- Is it a strong or weak relationship
- Are there other variables at work
- The more the dots look like a line the stronger the relationship.
e.g. income vs Happiness
Scatterplots
Linearity can described in two ways:
* Magnitude.
- i.e., strength.
* Direction.
- Positive or negative.
Null Hypothesis Significance Test
- Also NHST
- Tests if sampling error is responsible for correlation
- Tied to sample size - the bigger sample the better likleyhood that difference is significant
- How likely is our result if the variables are unrelated in the real world
Effect Size
- How practically meaningful a result is is
- regardless of its significance
NHST - Formula
- H0: r = 0
- Variables are independent.
- r > 0 is due to sample error.
- H1: r ≠ 0 (two tailed); r > 1 or < 1 (one tailed).
- Variables are correlated
Cohen’s Effect Size
Cohen’s (1988) Conventions for Psychological Research:
1. Large: > .50
2. Moderate: Approximately .30
3. Small: Approximately .10
Look at magnitude/size of the correlation
* Anything above 0.05 is a large correlation or effect
* Around 0.32 is moderate correlation
* between 0.12 and .3 is a small correlation
Power Tables
- Important to consider when evaluating effects
- Need to assess if your measure has been properly tested
- This measures your effect based on sample size.
- The smaller the anticipated effect the larger the sample size you require
Reliability Coefficient
- Must not apply Power Tables too rigidly
- r = .50 would be a poor measure
- Would not use the scale
- Correlation Coefficients need to be put into context
Rosenthal 1995 - Correlation Coefficient
- Physicians identify most important medical breakthrough.
- Most popular was drugg cyclosporine- reduces organ donation rejection
- The relationship between patient survival and use of drug showed r = .15.
- This small correlation actually saved thousands of lives
- Needs to be interpreted in context
Factors Affecting Magnitude of Correlation
- Reliability of Measures
- Outliers
- Restriction of Range
Reliability of Measures
- The extent of a measure producing stable & consistent scores over time
- Not influenced by random errors
- Unreliable measures reduce the size of the correlation
Non Linearity
where there is not a straight-line or direct relationship between variables
Restriction of Range
- Variable has less variability in a sample than in the full population.
- Restricted range can be present for observed variables or in other variables that were not measured.
- Scores outside of a cenratin range can change the size of the effect
Pearson’s R
- Most common statistic for correlation
- Indexes the degree of linearity only
- Not related to the slope of the line. if there is one.
- Measure of the linear relationship between two variables
- r = 0 Not necessarily absence of relationship
Pearson’s R Magnitude
- Should not be confused with direction
- +.05 is the same magnitude as -.05
Bivariate Correlation
- Determine the existence of relationships between two different variables
- Correlation does not equal Causation
- Two correlated variables does not mean they cause one another
- Global Warming does not decrease the number of pirates