Lead zero in decimals

Is a lead zero used before a decimal point? Consider the following example:

a) ...a modest improvement in A1C of .5% to 1%.

b) ...a modest improvement in A1C of 0.5% to 1%.

AMA Style prefers (b) — numerical values less than 1 typically require the lead zero. Exceptions include, (in)famously, P values and (lesser known) alpha levels.

Click here for an explanation of P values in AMA.