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 theory

– Unique or rare cases

– Representative cases

– Longitudinal case – time series

GOOD AND BAD CASE STUDIES Plan your study!

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)

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 interrater reliability

Yin (2009) © Nevit Dilmen via Wikimedia Commons

Internal validity

• Establish causal relationships, distinguished from spurious relationships

– Pattern matching

– Explanation building

– Addressing rival explanations

– Using logic models

Yin (2009)

ANALYZING THE DATA

Pattern Matching

• Put the info into different arrays

• Make a matrix of categories

• Graphically analyze the data

• Count!

• Do stats

• Use time

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

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

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 case

• the effect size for the difference between the case and controls

Careful with inflation of type 1 error!

Crawford et al., 2010

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