In general, for estimation, the more observations the better. This suggests using as long a time
period as possible. With a long estimation period for beta, however, it is likely that the value of
the true beta changes over the period. The resulting estimate for beta will, therefore, be biased.
This pulls us in the direction of shortening the period. One way of obtaining more observations,
over a shorter time period, is to increase the sampling frequency. However moving from
monthly to daily returns, for example, results in an increase in the amount of noise in the data,
which reduces the efficiency of the estimates. Thus there is a trade off between the length of the
time period and sampling frequency. In this paper, therefore, the performance of monthly data
for five years (the standard data frequency and time period used), weekly data for two years, and
daily data for one year, are examined