Correlational studies involve the collecting data for two or more variables from each participant. There is no manipulation of an independent measure and therefore the purpose of a correlational study is not to demonstrate a causal relationship between the two but simply to say that they are or are not related to one another. 
Ramirez-Esparza and colleagues (2017) examined the correlation between the amount of parentese used with infants aged eleven months and language development at both 24 and 33 months. The researchers found a significant positive correlation.

Activity: Sketch a scatter diagram to show the findings of the study by Ramirez-Esparza and colleagues (2017). Label your axes carefully and make sure you give our sketch an informative title. Why couldn’t the researchers conclude that lack of parentese is a cause of language impairment? Finally, can you think of a covariables that might be negatively correlated with language development , e.g. something that might mean a child does not make such good progress in language acquisition?