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Subject:

Walter's test for seasonality

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Date:

Thu, 28 Oct 1999 13:32:41 -0400 (EDT)

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 ``` Dear all, Is there anybody with experience of Edwards test for seasonality with a variable population at risk as described by Walter and Elwoods. I refer particularly to the estimate of the amplitude of a simple harmonic trend. I am constantly overestimating this and wonder whether my interpretation of the estimate is wrong. As far as i know, the estimate for alpha is: Alpha= 2*[d*sqrt(k*M)-sum[sqrt(mi)*cos(thetai-thetastar)] all divided by sum[sqrt(mi)*cos(thetai-thetastar)^2] where d is the distance of the sample centre of gravity from zero. k is the number of sectors (in my case twelve) M is the total population at risk mi is the population at risk per month thetai is the monthly midangle and thetastar is the estimate of the direction for the maximum rate In short, is this correct (for instance where does the '2' come from; my expansion abilities are not very good). If not, any suggestions why my estimates of the amplitude are so incorrect. (and thus i cannot calculate the goodness of fit statistic, which is what i really want). I am using excel to calculate it and it has been checked thoroughly to see if it is holding the right formulae. Any answers fully appreciated Thanks Paul ----------------------------------- Paul Wicks [log in to unmask] St. Georges Hospital Medical School %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% ```