Let me make it clear by make an example:
Suppose I knew a person's cost each month for 3 years like:
2016Jan : $2500
2016Feb : $4000
2016Mar : $3500
Just according to this, can I predict how much he earned each month in these years? If I could, what model should use? If I couldn't, what info I need to make this possible. If I couldn't guess in 100 percent but I could guess by some probability, what model should I use?
Another example: Need to estimate how much each store sells in each city, however I could only got the sales when they record it in electric system, if they didn't record it in electric system(may use paper or something else); then I don't know, how can I get all sales, not just the sales record in electric system?
Any suggestion is welcomed