Your filter in the query is based on the result of the Row_number function in the sub query. That filter based on the order of [Field2], [Field3], [Field4] by partitioning [Field2], [Field3]. In other words only columns [Field2], [Field3], [Field4] influance the Row_number results. If the results are not the same each each execution that mean that your Row_number function order the rows each time in different order. This can be if you have more then one row with the same values for these column [Field2], [Field3], [Field4]. In this case if you want to get the same result each time you need to find another parameter for the sorting, one that is unique. For example you can add [Field1] to the sorting order (I assume that [Field1] is identity column). But in your case you do not show us or return the result of ROW_NUMBER so using ht final filter "Where ID > 1" might return more then one row of the same group.
Controlled experiments can be performed when it is difficult to exactly control all the conditions in an experiment. In this case, the experiment begins by creating two or more sample groups that are probabilistically equivalent, which means that measurements of traits should be similar among the groups and that the groups should respond in the same manner if given the same treatment. This equivalency is determined by statistical methods that take into account the amount of variation between individuals and the number of individuals in each group. In fields such as microbiology and chemistry , where there is very little variation between individuals and the group size is easily in the millions, these statistical methods are often bypassed and simply splitting a solution into equal parts is assumed to produce identical sample groups.