I have two time-series of 2 different products `x & y`

. They belong to the same main category, e.g.: Iphone 6 and Iphone 5. Maybe one product is the predecessor of the other product.

I tested for correlation between the sales of the 2 products and got `r=.67`

. Correlation is calculated on the number of sales of the 2 products for the same month. Does this mean that there is a causal relationsship between the sales of the two products?

Are both sales pattern the same? In this case I might be able to forecast one time series with the historical data of the other one.

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#### Best Answer

You informed us that these are two *extremely* different products. If there is no theoretical reason *at all* for sales to be correlated and you still find a strong correlation, it is likely that there is a spurious relationship. I would like to remind you that this is a bivariate analysis, and the interpretation of the relationship between sales would remain limited unless you extend it to multivariate framework (by including other predictors, controls etc.).

After edit:

I think the argument still holds. Without accounting for other factors (with additional assumptions), looking only to correlation between sale numbers (for a month) to make predictions about future would be misleading. Maybe reading more on forecasting will be a better strategy, this website might be helpful.

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