In psychology there's as much of a replication problem as there is in biology, or in chemistry. Psychologists don't have a special problem on their hands. We have the same problem as every other scientific field and that when something is true with a capital t, it should hold under any circumstances,. regardless. If i test you on a day where you got eight our sleep, verseus a day wer the night before you got four hours sleep, it's going to effect your performance. In fact, there are some studies which estimate that you lose like a full ten points, like a full standard evihition on an ic test, if you're tested after a sleepless night.