PTAT number decreasing?

[b]

I placed an advertisement for my facebook page and I ended up with 55 likes and 41 people talking about this. However, when i ended the advert, the PTAT number dropped to 35 ppl and just two days ago it dropped again to 30. Once the number was increasing now it seems to be decreasing! Why is this happening? Is this something to do with the advert expiring? I post things to my page almost every day and my posts get a lot a clicks? Grateful for any explanation.

[philyoung123]

It could be because they have clicked the "stop notification" button on the advert