I have a *very* large dataset (n>300,000 rows) of water readings in this format;

Reading1; Date1; Reading 2; Date 2; Reading3; Date3 etc

50Kl; 23/04/06; 122Kl; 23/07/06; 45Kl; 25/10/06

Two datasets have 16 columns each as above, and one has 30 columns (Biannually 2006 - 2009 and Quarterly 2006 - 2009). Each reading is taken at the following date, and reflects the water use until that day (ie. Reading 2 is all the water used between Dates 1 and 2).

What I want to do is analyse change over time, how water consumption reduced over the period. Also, look at dates of implementation of policy, and see if water consumption figures "responded" accordingly. I also want to aggregate water consumption to an areal (census) measure, to analyse this against Census data; and look at the significance of various other variables, such as land value and lot size.

I know I can do a Repeated Measures for some of this; but the problem I have is that all dates of reading are NOT the same, and might differ by up to two months. i.e. under the column Date 1, are many different dates.

I haven't the vaguest idea where to start, so any help is greatly appreciated!!!!