Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of retailer Conn's (CONN 4.61%) jumped on Tuesday after the company reported its fourth-quarter earnings. By 2:15 PM, the stock was up about 9%, after jumping nearly 18% earlier in the day.

So what: Conn's reported revenue growth of 18.2% during the fourth quarter, driven mainly by new store openings. Same-store sales increased by just 1.3% during the quarter, but Conn's still managed to beat analyst estimates for revenue.

EPS fell dramatically year-over-year, coming in at $0.42 for the fourth quarter, down from $0.75 during the same period last year. Losses related to Conn's credit business, where it extends loans to customers, grew year-over-year, reducing profitability.

The 60-day delinquency rate for Conn's loan portfolio came in at 9.7% during the fourth quarter, up from 8.8% one year ago. This number improved in February, however, falling to 9.2%. Going forward, Conn's expects same-store sales to be flat or up in the low single-digits during fiscal 2016, a far cry from the rapid growth Conn's experienced over the past few years.

Now what: The stock's rise is likely due to the delinquency rate moving in the right direction. Last year, Conn's took a huge charge related to its credit business, and worries over the quality of its loan portfolio have driven the stock down over the past year.

The delinquency rate is elevated compared to past years, however, and the credit business is still deteriorating. For the full year, the credit business posted a loss of $62.8 million, compared to a profit of $12.5 million during the previous year. Growth is being driven by new store openings, and since nearly 80% of sales are financed directly, the resulting negative free cash flow has led to a rapid rise in debt.

Conn's earnings show that the delinquency situation is under control for now, and the market reacted positively. But I have serious doubts about the quality of Conn's loan portfolio and the sustainability of its business model.