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I am trying to catch changes in customers sales from week to week using R.

Historical.stats <- ddply(Historical, .(Company,Customer), summarise, mean= mean(Sales), lowerlimit = quantile(Sales,.05) ,higherlimit = quantile(Sales,.95), pval=t.test(Sales,data=Historical)$p.value)

My first attempt at doing this was to use the Quantile and then merge by Current Week data by the Company and Customer. I then would check if the sales this week were above or below the lower and higher quantiles.

dat <- merge(CurrentWeek, Historical.stats, by = c("Company","Customer"))
dat$plot <- ifelse((dat$Sales< dat$lowerlimit | dat$Sales> dat$higherlimit) ,1 ,0)

After doing more research would it be best to use something like the Levine test, a standard t.test or some type of ANOVA method to do this type of anomaly detection. I understand I won't be able to take into account seasonality or holidays.

Example Data
Company   Customer   Week   Sales
Company A Customer 1 05/07/2014 100
Company A Customer 2 05/07/2014 50
Company B Customer 1 05/07/2014 200
Company B Customer 2 05/07/2014 150
Company A Customer 1 05/14/2014 20
Company A Customer 2 05/14/2014 20
Company B Customer 1 05/14/2014 100
Company B Customer 2 05/14/2014 50
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