Which data step correctly calculates the difference in Tavg between consecutive rows?

To understand why the chosen answer is correct, it is important to note that the objective is to calculate the difference in Tavg between consecutive rows of data. The correct approach effectively uses the lag function to reference the previous value of Tavg and then computes the desired difference.

In answer C, the code first uses the lag function to retrieve the value of Tavg from the previous observation and stores it in a variable called Day1. This process allows you to access the most recently recorded average temperature before the current row. Next, it checks if the current observation is not the first one by using the condition _N_ > 1. When this condition is true, it calculates the difference between the current Tavg and the value stored in Day1, thus providing the correct difference between consecutive rows. This method ensures consistency and correctness in referencing past values in the dataset.

The approach in answer C is clear and structured, protecting against issues that may arise from directly manipulating the Tavg variable without storing the lagged value separately. This makes it straightforward to understand and prevents potential errors that could occur by referencing Tavg too directly.

By using this methodology, the solution fulfills the requirement of calculating differences effectively while maintaining the integrity of data flow throughout the data