The quarterly sales levels for the past four years of a leading tyre manufacturer are displayed on the table
How to analyze the data to determine the specific seasonal indices,and what conclusion can be deduced from the results?
Generally after $Q2$(second quarter) i notice a slight decrease in manufacturing ,which implies the relationship is not linear,and also with the average production for each season being respectively $2397,2623,2537,2645$,
i would like to know how further this data can be analyzed and how to obtain sales for the next quarter of 2013(assuming that cyclical and irregular components are negligible)
I'm not sure what type of analysis you want/need to do. One thing you may do is to do a linear regression analysis on the sales of each quarter $Q_1,..,Q_4$, and from the model for each $Q_i$, extrapolate into $2013$. There are other techniques you can use, like $ANOVA$ , where you test whether the means for sales in different quarters are different at a given significance level. Please let me know if this is what you're looking for.