Based on your description that the line is "decreasing" but looks messy, the vocabulary words that can be used to describe the data represented in the scatterplot are:
- Bivariate - because the scatterplot represents the relationship between two variables (age and number of times cried).
- Decreasing - since you've mentioned that the line is decreasing, meaning as age increases, the average number of times a student cried each month decreases.
- Linear trend - if the overall trend seems to generally follow a linear pattern despite being messy.
While "increasing," "positive trend," "univariate," and "proportional" are not suitable given your description.