Assuming we are dealing with a simple random sample of size 5, we can calculate the variance and standard deviation of the data set using the following formulas:

- Variance: s^2 = Σ(xi - x̄)^2 / (n - 1) 
- Standard deviation: s = √(Σ(xi - x̄)^2 / (n - 1))

where xi is each data point, x̄ is the mean of the data set, and n is the sample size.

Using these formulas, we get:

- Variance: s^2 = [(15-17.0)^2 + (18-17.0)^2 + (21-17.0)^2 + (12-17.0)^2 + (19-17.0)^2] / (5 - 1) = 16.5
- Standard deviation: s = √(16.5) = 4.06

So, one possible prediction using standard deviation and variance is that future data points will most likely fall within ±1 standard deviation of the mean of 17, which is between 12.94 and 21.06.
15, 18, 21, 12, 19
Genera una previsione per i seguenti dati di serie temporali. Usa la deviazione standard e la varianza.