Jasper Corporation Is Preparing Its Year-End Financial Statements and Needs

Jasper Corporation is preparing its year-end financial statements and needs your assistance evaluating the following items:
1. When recording the current year depreciation expense, the controller noticed that depreciation expense recorded in the prior year did not consider the residual value into the calculation.
2. Management has decided to change the method used to depreciate the company's equipment from double-declining balance to straight-line method because of a change in the pattern of benefits received from the assets.
3. Management has changed the rate used to calculate the company's estimated warranty liability.
4. After defending a legal dispute relating to its patent, the company reduced the patent's amortization period.
Instructions
a) Analyze each of the four events described above and identify the type of accounting change that has occurred.
b) Indicate whether each event above should be accounted for retrospectively or prospectively.