Data science up for first round of review

1) Focus on rspec tests 
2) Stuck at trying to refactor the exception part
You shouldn't need to do print_calculated_values. This can use the to_s convention to print the method returns directly:
<pre>
def to_s
# If you need them to be on separate lines:
  "Conversion rate #{conversion_rate}\n Standard error #{standard_error}\n Confidence  #{confidence}"
end

# otherwise you can call this from outside the instance in an external method that does the printing you want, and simply calling the instance methods 
puts "#{instanceName.conversion_rate}" ...
</pre>