Research Methods D Flashcards
1) Weak, 2) moderate and 3) strong bivariate correlations
1) .1-.3
2) .3-.6
3) .7-.9
(sign doesn’t influence strength)
When to use Pearson’s r and Spearman’s rho
Pearson’s when parametric, Spearman’s when non-parametric
Complications in correlations (5)
Small samples (under 10) unreliable Non-normal distributions Outliers (are they omitted?) Non-linear relationships Hetrogenous samples
Example of hetrogenous sample
If r=.5, but for men and women in sample r=.12 and r=.14 respectively…
separate correlations produce much weaker scores but together form a moderate correlation
How correlation explains the variance
Can be used to see how much the variation of scores in the data are explained by the study… showing the overlap on a ven-diagram. Use R^2 for this
If r=.7, how much of the variance is explained?
.7 x .7 = .47, so R^2 = .49, so 49% of variance is explained
How to make simple correlations more inline with reality’s complexity
Partial out (control for) other theoretically driven causal or confounding variables when analysing
How to decide when to use 1) more or 2) fewer questions in a questionnaire
Use more when dealing with: complex concepts, attitudes/beliefs or psychometric factors
Use less when: only a few dimensions, concepts are well defined and for attributes / behaviours
key principles of questionnaires (3)
test-retest reliability
Addresses intended concept (validity)
Can be meaningfully, quantitatively, analysed
How to solve problem of acquiescent or socially desirable respondents of questionnaires (3)
Invert some questions (back-to-front coding)
Include contradictory statements to see if they answer the same
Include dummy / masker questions to make the topic of questionnaire subtler (social desirability reduced)
How to do questionnaire data entry (2)
Each participant gets a row, each item getting a column
Data must be typed in raw (no altercations)
Why negative items must be reverse coded
So all items point the same direction, the top score conceptually meaning the same thing
Reliability
Extent that the measure is stable / consistent, and produces similar results when administered repeatedly
How to test questionnaire reliability (3)
Test-retest
Split-half - giving half of questions to one group and half to the other
Item analysis (the best) - sorts the useful and non useful questions (tests internal consistency)
Describe Cronbach’s alpha in item analysis
If items on questionnaire fit together coherently, the Cronbach’s alpha will be closer to 1. If = 1, all items will have been answered the exact same
Describe correlations in item analysis
If an item makes a useful contribution to a questionnaire, its score will correlate with the questionnaire total.
If it does not, this reduces the alpha so may want to be removed
How to conduct an item analysis with the correlations and Cronbach’s alpha
Use the item total statistic (how much it correlates to questionnaire score) to decide which item to recode or delete, repeat an item analysis after each change until Cronbach’s alpha is: .7 < alpha < .8…. but preferably closer to .7.
Start by recoding the most negative items and then deleting the smallest correlations - also refer to ‘alpha if deleted’ column
(NEVER recode an item twice)
What the item total statistic can tell you in item analysis if negative (and moderate-strong)
It is measuring the conceptual opposite of what was intended
What the item total statistic can tell you in item analysis if low
The item does not differentiate between people, everybody giving the same answer… question could display too extreme a view, or too common a belief
What the item total statistic can tell you in item analysis if low and the alpha increases if deleted
Question does not measure the intended thing, it lacks relevance… answers look random on graph comparing to overall questionnaire score
Known groups validity and how to test
Differing scores found for groups already known to differ
Test with a t-test
Concurrent validity
New scale compares to the established ‘gold standard’ measure (already reliably tested) - about its predictive power against other questionnaire
Construct validity
Appears consistent with theories of construct the questionnaire is interested in
Content validity
If all aspects of the content appear reflected (and proportionally reflected) in the questionnaire
Criterion validity and e.g.
Results are consistent with other measures, matching theory. e.g. IQ tests designed to correlate with child’s age
Face vailidity
If experts, participants (etc) agree that the construct is being accurately measured
Relationship between reliability and validity
Without reliability, there can be no validity… if results do not show a consistent pattern then the concepts could not have been measured
Describe factor analysis conceptually (3)
Correlates all items on the questionnaire in all possible combinations
Can then see what item’s correlations cluster together, these have something in common… meaning they explain the same part of the variance
Qualitatively decide on a label to give these clusters based on features of the questions
Why having factors in a questionnaire is useful (2) and not useful (1)
Makes the overall topic more subtle
Gives a greater understanding of scores
Not useful as makes the analysis more complicated
Steps of factor analysis from the output
Use scree plot to decide how many factors are needed
Construct the basic factors
Rotate factors, so they make more ‘sense’
Label the factors (ideally unrelated to each other)
Factor loadings
How much each item relates to factor, if it correlates to it then it relates to it
Scree plot
Graphical representation of effectiveness of each factor, showing how much variance is explained. Generally, should use if greater than 1.
What is the factor loading threshold for an item belonging to a factor
Is arbitrary but around .4 - .5
What to do if item belongs to more than one factor
Make a judgement which to include it in depending on size of factor loading, and then depending on qualitative relatedness to each factor (can belong to both factors!)
Rotation in factor analysis
Graphically, turn the factors x and y axis together, keeping perpendicular… until scores are nothing for one factor and more so for the other (increasing simplicity)
If done for all factors… are proportionally the same still
What to do with negative factor loadings
They are still members of the factor as if they were positive.
What to do with upside-down factors
If majority / all of its factor loadings are negative, be aware of what this is saying when creating a label
How to get the best factor analysis
Re-do it with differing numbers of factors depending on scree plot (especially when borderline close to 1), until satisfied with the labels and loadings etc
How to label factors (2)
Use the size and direction of loadings to determine label, they show significance of each item
Look at meaning of items together, label going beyond just one item
Steps to creating a questionnaire (4)
Item pool - defining concept and creating questions
Pilot testing - sees if it asks what we intend
Reliability check - test-retest / item analysis
Validity check - e.g. discriminative
Purpose of factor analysis (2)
Informs about the underlying structure of the construct being measured
Shows how participants conceptualise items
Benefit of a 4-point likert scale
Forces choice to either agree or disagree
Convergent validity
Correlation of results with an existing questionnaire
Incremental validity
How the questionnaire is distinguished from other measures
Why we use correlations (4)
To show reliability (e.g. test-retest)
Predict the outcome of one variable on another
To show validity
Theoretical verification
What R^2 is diagrammatically equivalent to
the overlap on a ven diagram
What does the ‘variance explained’ tell us
R^2 shows how accurate the model is based on its predictive power
How correlation can be closer to being causal evidence
If supported by theoretical or observational inputs that can explain how there are no / little other variables to effect the association
What is the criterion
The dependent variable, what we predict (y-axis)
What is the predictor
The independent variable, what we are predicting from (x-axis)