A group of scientists are interested in finding out whether the days of rainfall during the dry season could predict the magnitude of butterfly migration in the local area during wet season. Every year for twenty years, they count the total days of rainfall during the dry season preceding the migration and measure the number of butterflies migrating in the following wet season. Which type of statistical test should they use to analyze their data?

1. Paired samples t test
2. One-way ANOVA
3. Single sample t test
4. Independent samples t test
5. Simple linear regression
6. Z test
7. Pearson's r correlation