Previous research has shown that 8-hour urine collection does indeed produce results paralleling the 24-hour collection, and recent research also demonstrates concordance between 12-hour and 24-hour urine collections. That said, both these studies were based on small sample populations, fewer than 100 women. Another study of women with preeclampsia showed good correlation between the results of urinary protein in samples collected over 12 hours at night and those collected over 12 hours during daytime.