However, other sociologists point out that religious factors can explain high Muslim birthrates. Surveys indicate that Muslims in India have been relatively less willing to adopt family planning measures and that Muslim women have a larger fertility period since they get married at a much younger age compared to Hindu women.[122] On the other hand, it is also documented that Muslims tend to adopt family planning measures.[123] A study conducted by K.C. Zacharia in Kerala in 1983 revealed that on average, the number of children born to a Muslim woman was 4.1 while a Hindu woman gave birth to only 2.9 children. Religious customs and marriage practices were cited as some of the reasons behind the high Muslim birth rate.[124] According to Paul Kurtz, Muslims in India are much more resistant to modern contraception than are Hindus and, as a consequence, the decline in fertility rate among Hindu women is much higher compared to that of Muslim women.[125][126] The National Family and Health survey conducted in 1998–99 highlighted that Indian Muslim couples consider a substantially higher number of children to be ideal for a family as compared to Hindu couples in India.[127] The same survey also pointed out that percentage of couples actively using family planning measures was more than 49% among Hindus against 37% among Muslims.