Alocal supermarket organised two weeks of promotions to boost sales. the average dailly salles before the carmpaign is $10 000, which becomes $11 000 during the promotion (average over 2 weeks). which analysis below is not useful for evaluating whether the increase in sales is statistically significant?

1. check the distribution of sales data.
2. inspect for possible outliers in sales data.
3. calculate precision of the prediction
4. monitor sales for longer period of time.