Do taller toddlers have larger vocabulary? Why could it be so?
Positive correlation, not causal.
Practice makes perfect
We want to find out if the height of a toddler is correlated to the size of their vocabulary. Let's pay close attention to this situation.
Is There a Correlation?
Does the height of a toddler correlate to the size of their vocabulary? More often than not, taller toddlers will have a larger vocabulary. The line of fit would probably look something like the graph below.
Notice that the domain can only be values within the first quadrant. The height of a toddler and their vocabulary size cannot be negative. Also, toddlers cannot have a height of 0. In fact, an average height of a newborn child is between 18 and 22 inches. Therefore, we know the graph starts at some positive height. Looking at the graph, we can say this is a positive correlation.
Is the Relationship Causal?
Notice that a positive correlation here does not mean that gaining an inch in height will cause a change in the vocabulary size of a toddler. This is not a causal relationship. Remember that correlation does not imply causation! The most plausible explanation here is that taller kids are more often older and humans learn more words as they age.
