A total number of 104 fieldstone churches were built between the 13th and 16th century, of which 83 have been preserved.
"[2] Until Hiekkanen's research, which is based in statistical interpretation of field observations using "a systematic database of comparative criteria,"[3] most of the churches were generally considered 100–200 years older.
While Hiekkanen's dates represent those most frequently used by state museums[4] and the Finnish Heritage Agency, his work is not universally accepted and scholars have disagreed with various elements of his research, including his methods and certain dates offered.
Åsa Ringbom of Åbo Akademi University, an art historian and one of the principal researchers of the Åland Churches Project, has offered dates for the construction of the stone churches of Åland that, in some cases, differ from Hiekkanen's by a century or more.
Hiekkanen has consistently dismissed the interdisciplinary methods used by Ringbom and his colleagues – which include a combined study of written sources, stylistic dating, archeological finds, dendrochronology, and mortar dating, among other modes – and, conversely, Ringbom has called into question Hiekkanen's lack of transparency regarding his methodological principals and limited incorporation of data which fall outside of his model.