When you can't or
won't run an
experiment (and still
want to study atypical
language development)
David Saldaña
Case studies: why do them
• A case study is not just the study of a case
• What makes a case:
– Critical cases for a theor...
Plan your study!

GOOD AND BAD CASE STUDIES
Construct validity
• Your measures should reflect what you say
you are measuring
– Multiple sources of evidence
– Others r...
Chain of evidence

Paper

Database

Protocol

Questions
External validity
• Where can your findings be generalized?
– Use theory
– Use replication logic across cases

Yin (2009)
Reliability
• Would someone else
find the same results
with the same
operations
– Detail a protocol
– Make sure you test
i...
Internal validity
• Establish causal relationships, distinguished
from spurious relationships
– Pattern matching
– Explana...
ANALYZING THE DATA
Pattern Matching
•
•
•
•
•
•

Put the info into different arrays
Make a matrix of categories
Graphically analyze the data
...
Pattern matching (more)
• Test predictions against your data – looking at
the DV:
– Predicted should happen
– NOT predicte...
Single-case studies:
• single-case studies typically employ a large
number of measures,
• more often than not these measur...
Effect sizes

Crawford et al., 2010
What should you report? At least
• the mean and standard deviation for controls
on the task
• the raw score of the single ...
Some software

http://homepages.abdn.ac.uk/j.crawford/pages/
dept/psychom.htm
Thank you

http://institucional.us.es/dcptea
http://personal.us.es/davsalsag/inicio.html
Case Studies: When you can't or  won't run an  experiment (and still  want to study atypical language development)
Case Studies: When you can't or  won't run an  experiment (and still  want to study atypical language development)
Case Studies: When you can't or  won't run an  experiment (and still  want to study atypical language development)
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Case Studies: When you can't or won't run an experiment (and still want to study atypical language development)

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Case Studies: When you can't or won't run an experiment (and still want to study atypical language development)

  1. 1. When you can't or won't run an experiment (and still want to study atypical language development) David Saldaña
  2. 2. Case studies: why do them • A case study is not just the study of a case • What makes a case: – Critical cases for a theory – Unique or rare cases – Representative cases – Longitudinal case – time series
  3. 3. Plan your study! GOOD AND BAD CASE STUDIES
  4. 4. Construct validity • Your measures should reflect what you say you are measuring – Multiple sources of evidence – Others review draft report – Chain of evidence Yin (2009)
  5. 5. Chain of evidence Paper Database Protocol Questions
  6. 6. External validity • Where can your findings be generalized? – Use theory – Use replication logic across cases Yin (2009)
  7. 7. Reliability • Would someone else find the same results with the same operations – Detail a protocol – Make sure you test interrater reliability Yin (2009) © Nevit Dilmen via Wikimedia Commons
  8. 8. Internal validity • Establish causal relationships, distinguished from spurious relationships – Pattern matching – Explanation building – Addressing rival explanations – Using logic models Yin (2009)
  9. 9. ANALYZING THE DATA
  10. 10. Pattern Matching • • • • • • Put the info into different arrays Make a matrix of categories Graphically analyze the data Count! Do stats Use time
  11. 11. Pattern matching (more) • Test predictions against your data – looking at the DV: – Predicted should happen – NOT predicted should NOT happen • Test independent variables against your data – looking at potential ID: – Predictor should be there – NON predictor should NOT be there • Find the simplest
  12. 12. Single-case studies: • single-case studies typically employ a large number of measures, • more often than not these measures are expressed on different metrics, • there is an emphasis on examining the profile (i.e., the relative strengths and weaknesses) • it is not uncommon for single-case studies to employ more than one control sample Crawford et al., 2010
  13. 13. Effect sizes Crawford et al., 2010
  14. 14. What should you report? At least • the mean and standard deviation for controls on the task • the raw score of the single case • the effect size for the difference between the case and controls Careful with inflation of type 1 error! Crawford et al., 2010
  15. 15. Some software http://homepages.abdn.ac.uk/j.crawford/pages/ dept/psychom.htm
  16. 16. Thank you http://institucional.us.es/dcptea http://personal.us.es/davsalsag/inicio.html

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