I found it : forgot a semicolon in the code
While[i <= 5,
sample = Table[RandomInteger[{1, 800}], {k, 1, sampleSize}];
Estimate[[j, i]] =
N[(sampleSize + 1)/sampleSize Max[sample] - 1, 3];
TracePrint[Estimate[[j, i]]];
i++
];
j++
] <--------------------------------------------- There ! Forgot it and you get {234' Null} With semicolon neatly {234}
Estimate ]
