For the second time in seven months, Toyota Motor Corp. and Ford Motor Co. both claim to produce the world's top-selling car. The clash shows how counting in the global automotive industry is complicated.

Ford said Tuesday that its Focus compact was the leading global nameplate with 1.02 million sales last year, citing R.L. Polk & Co. data that pegged Toyota's Corolla deliveries at 872,774. Toyota replied with a statement later the same day that claimed it sold 1.16 million Corollas.

Determining which company is correct isn't clear-cut. Tuesday's dispute followed a similar spat in August, when Ford claimed a six-month global sales lead for the Focus and cited IHS Automotive data that excluded some derivatives of the Corolla — such as the Matrix in the U.S., the Auris in Europe and the Verso in Japan. Analysts also calculate global sales differently on the basis of autos sold by joint-venture partners.