This is an appeal by claimant, Patricia Vernon, from an Industrial Commission order denying her claim for benefits. The issue, we address today is whether the commission’s ruling that claimant had not sustained her burden of proof in showing that her injury arose out of and in the course of employment is correct. We conclude the commission failed to adequately state how it ultimately came to its conclusion, and we, therefore, vacate its decision and remand.
Patricia Vernon had been employed by Omark Industries for approximately nine years working primarily as a material handler in the shipping department. Her work consisted of repeatedly moving and lifting wooden trays filled with primers, each tray weighing from twenty-eight pounds to in excess of fifty pounds. Claimant testified that some time in the middle of June, 1983, while at work, she started to experience *359pain in her lower back. She did not remember any particular incident that could have caused the onset of pain, nor could she pinpoint the day the pain began. She testified that she thought she first experienced it on the thirteenth of June, but acknowledged that it could have occurred either on June 14, or June 15. In her application for a hearing before the Industrial Commission, she stated that the date of injury was June 13, 1983 to June 23, 1983, during work hours.
Claimant did not immediately notify her supervisor of the incident. She was aware of the plant’s safety rules and shipping department regulations which require that any accident, no matter how small, be reported to the employee’s supervisor immediately. Claimant continued to work her normal work schedule until June 24, 1983, which was her day off. At that time she went to see Dr. Skinner, a chiropractor, for the pain in her back. The claimant was seen by Dr. Skinner on twelve occasions for treatment of her back condition. Feeling unsatisfied with Dr. Skinner’s treatment, the claimant visited Dr. A.G. Johnson, a general practitioner. Dr. Johnson prescribed Feldene to alleviate the back pain. After one week and no pain reduction, claimant scheduled an appointment with Dr. Colburn, an orthopedic surgeon. Claimant was examined in Dr. Colburn’s office by Betty Imthurn, a nurse practitioner. Claimant indicated to her that the onset of the pain occurred approximately five weeks before (middle of May, 1983) and was unrelated to any particular activity or incident. Claimant reported to have had low back pain off and on for at least five to six years. Imthurn directed the claimant to take several weeks off from work. Claimant notified her supervisor that she needed the time off, but did not then assert that it was needed as a result of any work-related accident or injury.
Claimant next visited Dr. Warren J. Adams of Spokane, Washington, whose speciality was orthopedic and spine surgery. Dr. Adams testified that the claimant stated she first noted back pain approximately six weeks earlier (around the middle of June) and before that had had no pain in her back or legs. Subsequently, at Dr. Adams’ direction, a myelogram and CT scan were performed on claimant. The test revealed a herniated disk for which Dr. Adams performed surgery. Claimant’s condition improved after the surgery and she was able to return to work by early January of 1984.
Claimant first notified her employer of an industrial accident on August 4, 1983, nearly two months after the initial onset of pain. She reported that she had a herniated disk in the low back caused by the lifting of wooden trays. Although claimant had been treated by Dr. Skinner beginning June 24, 1983, she did not report this treatment to her employer. She testified that she was attempting to take care of the problem herself, and was concerned that if the accident was reported she might be dismissed from her work or otherwise disciplined because she had had several other previous leaves of absence.
After a hearing before the Industrial Commission, the commission issued Findings of Fact, Conclusions of Law and Order on June 11, 1986. Aftey extensive statements of the facts (which are restated above) the commission made the following scant Conclusion of Law.
“The Claimant has not sustained her burden of proof that she suffered a personal injury to her back arising out of and in the course of her employment with Employer as she alleges in this proceeding.”
Our scope of review on appeal from the findings of the commission is well settled. We are to determine whether the commission’s factual findings are supported by substantial and competent evidence and, if so, we must affirm them. Idaho Const., art. 5 § 9, I.C. § 72-732, Neufeld v. Browning Ferris Industries, 109 Idaho 899, 712 P.2d 600 (1985). However, when questions of law are raised it is for this Court to decide them de novo. In the instant case, the commission did not explain the rule of law under which they were operating. They merely stated that the claimant did not meet her burden of proof.
*360We cannot ascertain whether the commission simply did not believe the testimony of the claimant’s doctors or her own testimony, or placed a greater weight on the conflicting evidence, or believed the claimant’s testimony, but applied a rule of law to reach its determination. It is not our function to guess the reasoning of the commission. We cannot determine that the commission acted properly, or improperly, in reaching its conclusion. Thus, we must vacate its decision and remand to clarify its rationale. With our restrained review of the commission’s factual findings, it becomes essential that the commission’s conclusions of law not be shrouded in ambiguity.
The commission has wide discretion in making factual determinations, and we will use a clearly erroneous standard in reviewing these determinations. However, before an appellate court can properly determine whether the commission’s findings were clearly erroneous, it must determine whether the correct legal standard governing the available discretionary alternatives was applied. Here, we do not know whether the commission simply disbelieved the claimant, or whether they believed the claimant but determined that a rule of law prevented her from sustaining her burden of proof. This decision cannot be made at the appellate level. As our Court of Appeals has stated in a similar context:
“However, it is one thing to hold that discretion has been exercised by reference to a misunderstood legal standard; it is quite another to usurp such discretion by deciding the issue anew at the appellate level. We have held that when a trial judge erroneously applies the law when making a discretionary decision, the appropriate appellate response is to remand the case for reconsideration under the clarified legal standard.” In the Matter of the Estate of Kunzler, 109 Idaho 350, 355, 707 P.2d 461, 466 (Ct.App.1985).
On remand, the issue the commission needs to focus on is whether the claimant sustained her burden of proving her injury resulted from an accident, as defined in I.C. § 72-102(14)(b), which arose out of and in the course of employment. The controlling law is contained in the worker’s compensation statutes. I.C. § 72-102(14) defines “injury” as a personal injury caused by an accident arising out of and in the course of employment. An “accident” is defined as “an unexpected, undesigned, and unlooked for mishap, or untoward event, connected with the industry in which it occurs, and which can be reasonably located as to time when and place where it occurred, causing an injury.” I.C. § 72-102(14)(b). Our case law indicates that the claimant’s proof must establish a probable, not merely a possible, connection to the cause and effect to support a contention that the compensable accident occurred. Callantine v. Blue Ribbon Linen Supply, 103 Idaho 734, 653 P.2d 455 (1982).
With this rule of law in mind, the commission must then examine the relevant facts to determine whether the claimant has sustained her burden of proof. As we stated in Neufeld:
“The determination of whether a particular injury arose out of and in the course of employment is a question of fact for the commission. [Citation omitted.] Such a determination necessarily involves weighing the evidence and assessing the credibility of the various witnesses, and is therefore committed to the expertise of the commission. The commission’s conclusions as to the weight and credibility of the evidence will not be disturbed on appeal unless they are clearly erroneous. [Citation omitted.]” Neufeld, supra, 109 Idaho at 902, 712 P.2d at 603.
To aid in appellate review, the commission must, when faced with contrasting factual allegations, find the facts, based upon the evidence it believes to be more credible. Here, the commission simply recited the conflicting evidence presented without resolving the factual conflicts. In short, the commission’s factual findings and conclusions of law are incomplete and need to be expanded before we can properly exercise our appellate review function. Accordingly, we vacate the commission’s *361decision and remand back to the commission with the instruction that it make more detailed factual findings and conclusions of law to support its ultimate holding.
Costs to appellant.
No attorney fees on appeal.
BAKES, BISTLINE and HUNTLEY, JJ., concurs. BENGTSON, J., pro tern, concurs in result.