Facebook Data Concern - facebook

Question

i have concern about the data returned from facebook api for reach, below is the JSON data i am gonna post:
{
"id": "0123456789/insights/page_impressions_unique/day",
"name": "page_impressions_unique",
"period": "day",
"values": [
{
"value": 54,
"end_time": "2014-08-16T07:00:00+0000"
},
{
"value": 6,
"end_time": "2014-08-17T07:00:00+0000"
},
{
"value": 2,
"end_time": "2014-08-18T07:00:00+0000"
}
],
"title": "Daily Total Reach",
"description": "Daily: The number of people who have seen any content associated with your Page. (Unique Users)"
},
{
"id": "0123456789/insights/page_impressions_by_age_gender_unique/day",
"name": "page_impressions_by_age_gender_unique",
"period": "day",
"values": [
{
"value": {
"F.35-44": 20,
"M.35-44": 11,
"F.25-34": 10,
"M.25-34": 5,
"F.55-64": 4,
"F.45-54": 4,
"F.18-24": 2,
"M.13-17": 1,
"M.65+": 1,
"M.45-54": 1,
"M.18-24": 1
},
"end_time": "2014-08-16T07:00:00+0000"
},
{
"value": [
],
"end_time": "2014-08-17T07:00:00+0000"
},
{
"value": [
],
"end_time": "2014-08-18T07:00:00+0000"
}
],
"title": "Daily Reach Demographics",
"description": "Daily: Total Page Reach by age and gender. (Unique Users)"
}
looking above data i get concerned,
the data for 16th for unique page reach is 54, and in demographic detail data the reach becomes on summing 60 for 16th,
similarly data returned from facebook for 17th and 18th are totally different.
why is it so? what should i do to get the proper data?